feat(ui): instance alarm override editor in InstanceConfigure

Adds an Alarm Overrides card to the per-instance Configure page (next to
the existing Attribute Overrides and Connection Bindings cards). Each
non-locked template alarm gets a row showing its trigger type, inherited
config, and inputs for an override JSON + priority override. A Clear
button removes the override; the Save Alarm Overrides button upserts
all dirty rows.

The HiLo merge / binary whole-replace semantics are surfaced via the JSON
placeholder hint per trigger type. Wired to the existing
InstanceService.SetAlarmOverrideAsync / DeleteAlarmOverrideAsync flow.

src/ScadaLink.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor

@@ -165,6 +165,76 @@
             </div>
         </div>
 
+        @* Alarm Overrides *@
+        <div class="card mb-3">
+            <div class="card-header py-2">
+                <strong>Alarm Overrides</strong>
+                <small class="text-muted ms-2">
+                    For HiLo alarms, override JSON merges into the inherited config setpoint-by-setpoint.
+                    For binary trigger types, override JSON replaces the whole config. Leave both fields empty to inherit.
+                </small>
+            </div>
+            <div class="card-body p-0">
+                @if (_overridableAlarms.Count == 0)
+                {
+                    <p class="text-muted small p-3 mb-0">No overridable (non-locked) alarms on this template.</p>
+                }
+                else
+                {
+                    <table class="table table-sm table-bordered mb-0">
+                        <thead class="table-light">
+                            <tr>
+                                <th>Alarm</th>
+                                <th style="width: 110px;">Trigger</th>
+                                <th>Inherited Config</th>
+                                <th style="width: 320px;">Override JSON</th>
+                                <th style="width: 120px;">Priority</th>
+                                <th style="width: 80px;"></th>
+                            </tr>
+                        </thead>
+                        <tbody>
+                            @foreach (var alarm in _overridableAlarms)
+                            {
+                                <tr>
+                                    <td class="small">@alarm.Name</td>
+                                    <td>
+                                        <span class="badge bg-light text-dark border">@alarm.TriggerType</span>
+                                    </td>
+                                    <td class="small text-muted text-truncate font-monospace" style="max-width: 280px;"
+                                        title="@alarm.TriggerConfiguration">
+                                        @(alarm.TriggerConfiguration ?? "—")
+                                    </td>
+                                    <td>
+                                        <input type="text" class="form-control form-control-sm font-monospace"
+                                               placeholder='@GetAlarmJsonPlaceholder(alarm.TriggerType)'
+                                               value="@GetAlarmOverrideJson(alarm.Name)"
+                                               @onchange="(e) => OnAlarmOverrideJsonChanged(alarm.Name, e)" />
+                                    </td>
+                                    <td>
+                                        <input type="number" min="0" max="1000" class="form-control form-control-sm"
+                                               placeholder="@alarm.PriorityLevel"
+                                               value="@GetAlarmOverridePriority(alarm.Name)"
+                                               @onchange="(e) => OnAlarmOverridePriorityChanged(alarm.Name, e)" />
+                                    </td>
+                                    <td>
+                                        @if (HasOverride(alarm.Name))
+                                        {
+                                            <button class="btn btn-outline-danger btn-sm"
+                                                    @onclick="() => ClearAlarmOverride(alarm.Name)"
+                                                    disabled="@_saving">Clear</button>
+                                        }
+                                    </td>
+                                </tr>
+                            }
+                        </tbody>
+                    </table>
+                    <div class="p-2">
+                        <button class="btn btn-success btn-sm" @onclick="SaveAlarmOverrides" disabled="@_saving">Save Alarm Overrides</button>
+                    </div>
+                }
+            </div>
+        </div>
+
         @* Area Assignment *@
         <div class="card mb-3">
             <div class="card-header py-2">
@@ -208,6 +278,15 @@
     private List<TemplateAttribute> _overrideAttrs = new();
     private Dictionary<string, string?> _overrideValues = new();
 
+    // Alarm overrides — keyed by alarm name. Dirty rows live in
+    // _alarmOverrideJson / _alarmOverridePriority; existing overrides are
+    // loaded via _existingAlarmOverrides so the UI can show inherited
+    // placeholders correctly.
+    private List<TemplateAlarm> _overridableAlarms = new();
+    private Dictionary<string, InstanceAlarmOverride> _existingAlarmOverrides = new();
+    private Dictionary<string, string?> _alarmOverrideJson = new();
+    private Dictionary<string, int?> _alarmOverridePriority = new();
+
     // Area
     private List<Area> _siteAreas = new();
     private int _reassignAreaId;
@@ -249,6 +328,19 @@
             var existingOverrides = await TemplateEngineRepository.GetOverridesByInstanceIdAsync(Id);
             foreach (var o in existingOverrides)
                 _overrideValues[o.AttributeName] = o.OverrideValue;
+
+            // Alarm overrides — load all non-locked template alarms and
+            // existing override rows. Pre-seed the dirty maps from existing
+            // values so the inputs render with what's currently saved.
+            var alarms = await TemplateEngineRepository.GetAlarmsByTemplateIdAsync(_instance.TemplateId);
+            _overridableAlarms = alarms.Where(a => !a.IsLocked).ToList();
+            var alarmOverrides = await TemplateEngineRepository.GetAlarmOverridesByInstanceIdAsync(Id);
+            foreach (var o in alarmOverrides)
+            {
+                _existingAlarmOverrides[o.AlarmCanonicalName] = o;
+                _alarmOverrideJson[o.AlarmCanonicalName] = o.TriggerConfigurationOverride;
+                _alarmOverridePriority[o.AlarmCanonicalName] = o.PriorityLevelOverride;
+            }
         }
         catch (Exception ex)
         {
@@ -333,6 +425,124 @@
         _saving = false;
     }
 
+    // ── Alarm overrides ─────────────────────────────────────
+
+    private bool HasOverride(string alarmName) =>
+        _existingAlarmOverrides.ContainsKey(alarmName);
+
+    private string? GetAlarmOverrideJson(string alarmName) =>
+        _alarmOverrideJson.GetValueOrDefault(alarmName);
+
+    private string? GetAlarmOverridePriority(string alarmName) =>
+        _alarmOverridePriority.GetValueOrDefault(alarmName)?.ToString();
+
+    /// <summary>
+    /// Placeholder hint shown in the JSON override input. Encourages the
+    /// HiLo "partial JSON" idiom (e.g. {"hi":90}) vs. the binary-trigger
+    /// "whole-config" idiom.
+    /// </summary>
+    private static string GetAlarmJsonPlaceholder(AlarmTriggerType type) => type switch
+    {
+        AlarmTriggerType.HiLo => "{\"hi\":90} — partial keys merge",
+        _ => "{\"attributeName\":\"...\"} — whole-replace"
+    };
+
+    private void OnAlarmOverrideJsonChanged(string alarmName, ChangeEventArgs e)
+    {
+        var val = e.Value?.ToString();
+        if (string.IsNullOrWhiteSpace(val))
+            _alarmOverrideJson.Remove(alarmName);
+        else
+            _alarmOverrideJson[alarmName] = val;
+    }
+
+    private void OnAlarmOverridePriorityChanged(string alarmName, ChangeEventArgs e)
+    {
+        var raw = e.Value?.ToString();
+        if (string.IsNullOrWhiteSpace(raw))
+        {
+            _alarmOverridePriority.Remove(alarmName);
+            return;
+        }
+        if (int.TryParse(raw, out var p))
+            _alarmOverridePriority[alarmName] = p;
+    }
+
+    private async Task ClearAlarmOverride(string alarmName)
+    {
+        _saving = true;
+        try
+        {
+            var user = await GetCurrentUserAsync();
+            var result = await InstanceService.DeleteAlarmOverrideAsync(Id, alarmName, user);
+            if (result.IsSuccess)
+            {
+                _existingAlarmOverrides.Remove(alarmName);
+                _alarmOverrideJson.Remove(alarmName);
+                _alarmOverridePriority.Remove(alarmName);
+                _toast.ShowSuccess($"Cleared override on '{alarmName}'.");
+            }
+            else
+            {
+                _toast.ShowError($"Clear failed: {result.Error}");
+            }
+        }
+        catch (Exception ex)
+        {
+            _toast.ShowError($"Clear failed: {ex.Message}");
+        }
+        _saving = false;
+    }
+
+    private async Task SaveAlarmOverrides()
+    {
+        _saving = true;
+        try
+        {
+            var user = await GetCurrentUserAsync();
+            var touched = _alarmOverrideJson.Keys
+                .Union(_alarmOverridePriority.Keys, StringComparer.Ordinal)
+                .Distinct()
+                .ToList();
+
+            var saved = 0;
+            foreach (var alarmName in touched)
+            {
+                var json = _alarmOverrideJson.GetValueOrDefault(alarmName);
+                var priority = _alarmOverridePriority.GetValueOrDefault(alarmName);
+
+                // If both fields are empty AND there's an existing override,
+                // clear it. Otherwise upsert (allows priority-only or json-only).
+                if (string.IsNullOrWhiteSpace(json) && !priority.HasValue)
+                {
+                    if (_existingAlarmOverrides.ContainsKey(alarmName))
+                    {
+                        await InstanceService.DeleteAlarmOverrideAsync(Id, alarmName, user);
+                        _existingAlarmOverrides.Remove(alarmName);
+                    }
+                    continue;
+                }
+
+                var result = await InstanceService.SetAlarmOverrideAsync(
+                    Id, alarmName, json, priority, user);
+                if (!result.IsSuccess)
+                {
+                    _toast.ShowError($"Save failed for '{alarmName}': {result.Error}");
+                    continue;
+                }
+                _existingAlarmOverrides[alarmName] = result.Value!;
+                saved++;
+            }
+
+            if (saved > 0) _toast.ShowSuccess($"Saved {saved} alarm override(s).");
+        }
+        catch (Exception ex)
+        {
+            _toast.ShowError($"Save alarm overrides failed: {ex.Message}");
+        }
+        _saving = false;
+    }
+
     // ── Area ────────────────────────────────────────────────
 
     private async Task ReassignArea()