feat(logging): Configure Serilog SQLite sink + UI

appsettings.json:
- Add Application:LogDirectory configuration
- Add Serilog WriteTo.SQLite sink (logs.db in LogDirectory)
- Logs table with UTC timestamps

Program.cs:
- Add Serilog.UI usings
- Configure Serilog.UI with SQLite provider
- Mount UI at /serilog-ui endpoint

Web-based log viewer accessible at: https://localhost:7186/serilog-ui

DocumentOperator.API/Program.cs

@@ -1,4 +1,7 @@
 using Serilog;
+using Serilog.Ui.Core.Extensions;
+using Serilog.Ui.SqliteDataProvider.Extensions;
+using Serilog.Ui.Web.Extensions;
 using DocumentOperator.Infrastructure.Configuration;
 using DocumentOperator.Application;
 using DocumentOperator.Infrastructure;
@@ -45,7 +48,23 @@ try
     builder.Services.AddSwaggerDocumentation();
 
     // ========================================
-    // 4. Build App
+    // 4. Serilog.UI Configuration
+    // ========================================
+    var logDirectory = builder.Configuration.GetValue<string>("Application:LogDirectory")
+        ?? throw new InvalidOperationException("Application:LogDirectory not found in configuration.");
+    var sqliteDbPath = Path.Combine(logDirectory, "logs.db");
+
+    builder.Services.AddSerilogUi(logUIOpt =>
+    {
+        logUIOpt.UseSqliteServer(dbOpt =>
+        {
+            dbOpt.WithConnectionString($"Data Source={sqliteDbPath}");
+            dbOpt.WithTable("Logs");
+        });
+    });
+
+    // ========================================
+    // 5. Build App
     // ========================================
     var app = builder.Build();
 
@@ -67,7 +86,12 @@ try
     app.UseHttpsRedirection();
 
     // ========================================
-    // 6. Endpoints (Controller-based API)
+    // 6. Serilog.UI Dashboard
+    // ========================================
+    app.UseSerilogUi(); // Accessible at /serilog-ui
+
+    // ========================================
+    // 7. Endpoints (Controller-based API)
     // ========================================
     app.MapControllers(); // Maps all [ApiController] controllers