backend: add force rescan parameter to scanner

- Add Force bool field to ScanLibraryRequest in handlers
- Pass force param through job params to worker
- Add forceRescan field and SetForce method to MediaScanner
- Modify processMediaFile to delete and re-create existing items when force=true
- Default behavior unchanged (force=false maintains skip-if-exists)

internal/services/worker.go

@@ -194,6 +194,11 @@ func (w *Worker) processScanJob(job *Job) (interface{}, error) {
 		return nil, fmt.Errorf("database queries required")
 	}
 
+	force := false
+	if forceVal, ok := job.Params["force"].(bool); ok {
+		force = forceVal
+	}
+
 	scanner := NewMediaScanner(db)
 	scanner.job = job
 
@@ -218,6 +223,7 @@ func (w *Worker) processScanJob(job *Job) (interface{}, error) {
 		return nil, err
 	}
 	scanner.SetAdminID(adminUUID)
+	scanner.SetForce(force)
 
 	if err := scanner.ScanFolders(job.Context); err != nil {
 		return nil, err