fix(client-ui): resolve Low code-review findings (Client.UI-003,004,006,009,010,011)

- Client.UI-003: wire Serilog properly per CLAUDE.md — console sink +
  rolling daily file sink in Program.Main, Log.CloseAndFlush in finally,
  per-VM Log.ForContext<> loggers.
- Client.UI-004: migrate the cert-store folder picker from the obsolete
  OpenFolderDialog to StorageProvider.OpenFolderPickerAsync (with
  TryGetFolderFromPathAsync seed + TryGetLocalPath extraction).
- Client.UI-006: surface formerly silent catch blocks via an observable
  StatusMessage on the Subscriptions / Alarms VMs that bubbles up into
  the shell's status bar; soft fallbacks log at Information level so
  hard failures stay distinguishable.
- Client.UI-009: docs/Client.UI.md now lists Standard Deviation in the
  Aggregate row of the Query Options table.
- Client.UI-010: removed the unused MinDateTimeProperty /
  MaxDateTimeProperty styled properties from DateTimeRangePicker.
- Client.UI-011: updated the cert-store TextBox watermark from the
  legacy AppData/LmxOpcUaClient/pki to the canonical
  AppData/OtOpcUaClient/pki.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Client/ZB.MOM.WW.OtOpcUa.Client.UI/ViewModels/AlarmsViewModel.cs

@@ -2,6 +2,7 @@ using System.Collections.ObjectModel;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using Opc.Ua;
+using Serilog;
 using ZB.MOM.WW.OtOpcUa.Client.Shared;
 using ZB.MOM.WW.OtOpcUa.Client.Shared.Models;
 using ZB.MOM.WW.OtOpcUa.Client.UI.Services;
@@ -13,9 +14,18 @@ namespace ZB.MOM.WW.OtOpcUa.Client.UI.ViewModels;
 /// </summary>
 public partial class AlarmsViewModel : ObservableObject
 {
+    private static readonly ILogger Logger = Log.ForContext<AlarmsViewModel>();
+
     private readonly IUiDispatcher _dispatcher;
     private readonly IOpcUaClientService _service;
 
+    /// <summary>
+    ///     Last user-visible status message — set when an alarm subscribe / unsubscribe / refresh
+    ///     operation fails so the shell can surface the diagnostic instead of silently dropping it.
+    ///     Genuine failures are distinguished from "feature not supported" (condition refresh).
+    /// </summary>
+    [ObservableProperty] private string? _statusMessage;
+
     [ObservableProperty] private int _interval = 1000;
 
     [ObservableProperty]
@@ -95,19 +105,25 @@ public partial class AlarmsViewModel : ObservableObject
 
             await _service.SubscribeAlarmsAsync(sourceNodeId, Interval);
             IsSubscribed = true;
+            StatusMessage = null;
 
             try
             {
                 await _service.RequestConditionRefreshAsync();
             }
-            catch
+            catch (Exception refreshEx)
             {
-                // Refresh not supported
+                // Condition refresh is optional on the server side — log at info level and surface
+                // a soft notice rather than a hard failure so the operator can tell apart "server
+                // does not advertise refresh" from a genuine subscribe failure.
+                Logger.Information(refreshEx, "RequestConditionRefresh not supported by server");
+                StatusMessage = "Condition refresh not supported by server (subscribed).";
             }
         }
-        catch
+        catch (Exception ex)
         {
-            // Subscribe failed
+            Logger.Warning(ex, "SubscribeAlarms failed for {Source}", MonitoredNodeIdText ?? "(all)");
+            StatusMessage = $"Subscribe to alarms failed: {ex.Message}";
         }
     }
 
@@ -123,10 +139,12 @@ public partial class AlarmsViewModel : ObservableObject
         {
             await _service.UnsubscribeAlarmsAsync();
             IsSubscribed = false;
+            StatusMessage = null;
         }
-        catch
+        catch (Exception ex)
         {
-            // Unsubscribe failed
+            Logger.Warning(ex, "UnsubscribeAlarms failed");
+            StatusMessage = $"Unsubscribe alarms failed: {ex.Message}";
         }
     }
 
@@ -136,10 +154,14 @@ public partial class AlarmsViewModel : ObservableObject
         try
         {
             await _service.RequestConditionRefreshAsync();
+            StatusMessage = null;
         }
-        catch
+        catch (Exception ex)
         {
-            // Refresh failed
+            // Same as the subscribe-time fallback: refresh is server-side optional. Information-
+            // level log + soft status so the operator sees why an explicit refresh did nothing.
+            Logger.Information(ex, "RequestConditionRefresh not supported by server");
+            StatusMessage = "Condition refresh not supported by server.";
         }
     }
 
@@ -189,19 +211,22 @@ public partial class AlarmsViewModel : ObservableObject
 
             await _service.SubscribeAlarmsAsync(nodeId, Interval);
             IsSubscribed = true;
+            StatusMessage = null;
 
             try
             {
                 await _service.RequestConditionRefreshAsync();
             }
-            catch
+            catch (Exception refreshEx)
             {
-                // Refresh not supported
+                Logger.Information(refreshEx, "RequestConditionRefresh not supported by server (restore path)");
+                StatusMessage = "Condition refresh not supported by server (restored subscription).";
             }
         }
-        catch
+        catch (Exception ex)
         {
-            // Subscribe failed
+            Logger.Warning(ex, "RestoreAlarmSubscription failed for {Source}", sourceNodeId);
+            StatusMessage = $"Restore alarm subscription failed: {ex.Message}";
         }
     }