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/sync/websocket.go

@@ -1,6 +1,7 @@
 package sync
 
 import (
+	"context"
 	"log"
 	"sync"
 	"time"
@@ -211,11 +212,21 @@ func (m *ConnectionManager) GetConnectionStats() map[string]int {
 }
 
 // StartCleanupTask starts a background task to cleanup stale connections
-func (m *ConnectionManager) StartCleanupTask() {
+func (m *ConnectionManager) StartCleanupTask() context.CancelFunc {
 	ticker := time.NewTicker(1 * time.Minute)
+	ctx, cancel := context.WithCancel(context.Background())
+
 	go func() {
-		for range ticker.C {
-			m.CleanupStaleConnections()
+		for {
+			select {
+			case <-ctx.Done():
+				ticker.Stop()
+				return
+			case <-ticker.C:
+				m.CleanupStaleConnections()
+			}
 		}
 	}()
+
+	return cancel
 }