refactor: Extract ProfileWorker into modular components

- Create ProfileWorker namespace with 4 separate components
- ProfileWorker.cs: BackgroundService orchestrator with IOptions support
- ProfileWorkerOptions.cs: Configuration model with validation
- ProfileCache.cs: Thread-safe cache using composition pattern
- DependencyInjection.cs: Service registration with IValidateOptions

Benefits:
- Separation of concerns (orchestration, config, state, DI)
- IOptions pattern for appsettings.json configuration
- Startup validation for configuration errors
- Better testability and maintainability

ECMJobRunner.WebCron/ProfileWorker/ProfileWorkerOptions.cs

@@ -0,0 +1,15 @@
+namespace ECMJobRunner.WebCron.ProfileWorker;
+
+/// <summary>
+/// Configuration options for ProfileWorker background service.
+/// </summary>
+public class ProfileWorkerOptions
+{
+    public const string SectionName = "ProfileWorker";
+
+    /// <summary>
+    /// Interval in milliseconds between profile synchronization checks.
+    /// Default: 1000ms (1 second)
+    /// </summary>
+    public int IntervalMS { get; set; } = 1000;
+}