Fix goroutine leaks in sync queue processor and connection manager

Critical fixes to prevent goroutine leaks during application shutdown:

1. Sync Queue Processor:
   - Changed StartCleanupTask() to return context.CancelFunc
   - Modified to accept and watch cancellable context
   - Added queue context/cancel to Handler struct
   - Created StartBackgroundTasks() method for main handler instance
   - Cancel queue processor during shutdown in StopScheduler()

2. Connection Manager:
   - Modified StartCleanupTask() to use cancellable context
   - Returns cancel function that can be called during shutdown
   - Goroutine now properly exits when context is cancelled

3. Handler Lifecycle:
   - Added StartBackgroundTasks() to Handler
   - Only main handler instance starts background goroutines
   - Temporary handler instances (library/sync routes) don't start tasks
   - StopScheduler() now properly shuts down all background goroutines

4. Router Integration:
   - Updated SetupRoutes to accept queueProcessor parameter
   - Main scanner handler starts background tasks after creation
   - Library and sync route handlers don't start duplicate tasks

Impact:
- Fixes 2 major goroutine leaks (queue processor + connection cleanup)
- Application now properly shuts down all goroutines on exit
- No more resource leaks from long-running goroutines
- Test added to detect future goroutine regressions

Test: TestGoroutineCleanup verifies background services can be stopped.

internal/router/router.go

@@ -133,7 +133,10 @@ func RegisterRoutes(cfg *Config) *handlers.Handler {
 	registerDocumentationRoutes(cfg)
 
 	// Create scanner handler for scanner routes and progress routes
-	scannerHandler := handlers.SetupRoutes(protected, cfg.Queries, cfg.ConnManager)
+	scannerHandler := handlers.SetupRoutes(protected, cfg.Queries, cfg.ConnManager, cfg.QueueProcessor)
+
+	// Start background tasks (queue processor and connection cleanup)
+	scannerHandler.StartBackgroundTasks()
 
 	// Register progress routes with actual handler
 	registerProgressRoutes(cfg, scannerHandler)