refactor(ui/design): replace JSON inputs with structured editors

Two new shared components in Components/Shared:
  - ParameterListEditor: table of rows (name + type + item type + required + remove)
  - ReturnTypeEditor: single type (+ item type when List)

Both round-trip the same JSON shape already stored on the entity:
  parameters: [{"name":"x","type":"String","required":true},...]
  return:     {"type":"List","itemType":"Integer"} | null

Type set follows the Inbound API validator (Boolean, Integer, Float,
String, Object, List). Legacy values normalize on read — Int32 / int64
/ Double / Decimal / lowercase string / etc all coalesce to the new
set so existing rows render correctly. Re-saving persists the
normalized form.

Applied to:
  - SharedScriptForm
  - TemplateEdit Add Script form (also surfaces ParameterDefinitions
    + ReturnDefinition which the entity supported but the form was
    never wiring through)
  - ApiMethodForm

Graceful degradation: invalid JSON is shown with a "Start fresh"
escape hatch instead of crashing the form.

src/ScadaLink.CentralUI/Components/Pages/Design/TemplateEdit.razor

@@ -85,6 +85,8 @@
     private string _scriptCode = string.Empty;
     private string? _scriptTriggerType;
     private string? _scriptTriggerConfig;
+    private string? _scriptParameters;
+    private string? _scriptReturn;
     private bool _scriptIsLocked;
     private string? _scriptFormError;
 
@@ -615,7 +617,7 @@
     {
         <div class="d-flex justify-content-between align-items-center mb-2">
             <h5 class="mb-0">Scripts</h5>
-            <button class="btn btn-primary btn-sm" @onclick="() => { _showScriptForm = true; _scriptFormError = null; _scriptName = string.Empty; _scriptCode = string.Empty; _scriptTriggerType = null; _scriptTriggerConfig = null; _scriptIsLocked = false; }">Add Script</button>
+            <button class="btn btn-primary btn-sm" @onclick="() => { _showScriptForm = true; _scriptFormError = null; _scriptName = string.Empty; _scriptCode = string.Empty; _scriptTriggerType = null; _scriptTriggerConfig = null; _scriptParameters = null; _scriptReturn = null; _scriptIsLocked = false; }">Add Script</button>
         </div>
 
         @if (_showScriptForm)
@@ -636,6 +638,14 @@
                             <label class="form-label">Trigger Config (JSON)</label>
                             <input type="text" class="form-control" @bind="_scriptTriggerConfig" />
                         </div>
+                        <div class="col-12">
+                            <label class="form-label">Parameters</label>
+                            <ParameterListEditor Json="@_scriptParameters" JsonChanged="@(v => _scriptParameters = v)" />
+                        </div>
+                        <div class="col-12">
+                            <label class="form-label">Return value</label>
+                            <ReturnTypeEditor Json="@_scriptReturn" JsonChanged="@(v => _scriptReturn = v)" />
+                        </div>
                         <div class="col-12">
                             <div class="form-check">
                                 <input class="form-check-input" type="checkbox" @bind="_scriptIsLocked" id="scriptLocked" />
@@ -884,6 +894,8 @@
         {
             TriggerType = _scriptTriggerType?.Trim(),
             TriggerConfiguration = _scriptTriggerConfig?.Trim(),
+            ParameterDefinitions = _scriptParameters,
+            ReturnDefinition = _scriptReturn,
             IsLocked = _scriptIsLocked
         };