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>

tests/Client/ZB.MOM.WW.OtOpcUa.Client.UI.Tests/MainWindowViewModelTests.cs

@@ -515,6 +515,25 @@ public class MainWindowViewModelTests
         _settingsService.LastSaved!.SubscribedNodes.ShouldContain("ns=2;s=TestSub");
     }
 
+    /// <summary>
+    /// Regression test for Client.UI-006 — when GetRedundancyInfoAsync throws (the server
+    /// does not implement the redundancy facet) the connection must still succeed and the
+    /// view model must leave RedundancyInfo null without crashing or hiding the diagnostic.
+    /// The Status text is expected to remain "Connected" (redundancy is optional).
+    /// </summary>
+    [Fact]
+    public async Task ConnectCommand_RedundancyFailure_DoesNotBreakConnection()
+    {
+        _service.RedundancyException = new Exception("BadServiceUnsupported");
+
+        await _vm.ConnectCommand.ExecuteAsync(null);
+
+        _vm.ConnectionState.ShouldBe(ConnectionState.Connected);
+        _vm.RedundancyInfo.ShouldBeNull();
+        // Connection succeeded; status reflects connection, not the optional redundancy probe failure
+        _vm.StatusMessage.ShouldContain("Connected");
+    }
+
     /// <summary>
     /// Verifies that saved subscriptions are restored after reconnecting the shell.
     /// </summary>