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/Program.cs

@@ -1,4 +1,6 @@
 using Avalonia;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Client.Shared;
 
 namespace ZB.MOM.WW.OtOpcUa.Client.UI;
 
@@ -7,8 +9,16 @@ public class Program
     [STAThread]
     public static void Main(string[] args)
     {
-        BuildAvaloniaApp()
-            .StartWithClassicDesktopLifetime(args);
+        ConfigureLogging();
+        try
+        {
+            BuildAvaloniaApp()
+                .StartWithClassicDesktopLifetime(args);
+        }
+        finally
+        {
+            Log.CloseAndFlush();
+        }
     }
 
     public static AppBuilder BuildAvaloniaApp()
@@ -18,4 +28,35 @@ public class Program
             .WithInterFont()
             .LogToTrace();
     }
+
+    /// <summary>
+    ///     Initializes the Serilog root logger with a console sink + a rolling daily file sink
+    ///     under <c>{LocalAppData}/OtOpcUaClient/logs/</c>. CLAUDE.md mandates Serilog with a
+    ///     rolling daily file sink as the project standard; this is also the only way the swallow
+    ///     blocks in the alarms / subscriptions / redundancy view-models surface a diagnosable
+    ///     trace when an operator hits a problem in the field.
+    /// </summary>
+    private static void ConfigureLogging()
+    {
+        var logsDir = Path.Combine(ClientStoragePaths.GetRoot(), "logs");
+        try
+        {
+            Directory.CreateDirectory(logsDir);
+        }
+        catch
+        {
+            // Best-effort; file sink will gracefully fall back if the dir can't be created.
+        }
+
+        Log.Logger = new LoggerConfiguration()
+            .MinimumLevel.Information()
+            .Enrich.FromLogContext()
+            .WriteTo.Console()
+            .WriteTo.File(
+                path: Path.Combine(logsDir, "client-ui-.log"),
+                rollingInterval: RollingInterval.Day,
+                retainedFileCountLimit: 14,
+                shared: true)
+            .CreateLogger();
+    }
 }