test: add unit and integration tests for scan settings

- Add unit tests for MediaScanner.GetPollInterval and GetAutoScanEnabled
- Add integration tests for scan-settings API endpoints
- Update validation test cases to use seconds (1-3600) instead of minutes
- Fix worker.go to use new NewMediaScanner signature

internal/services/worker.go

@@ -199,7 +199,7 @@ func (w *Worker) processScanJob(job *Job) (interface{}, error) {
 		force = forceVal
 	}
 
-	scanner := NewMediaScanner(db, 0)
+	scanner := NewMediaScanner(db)
 	scanner.job = job
 
 	job.ProgressCallback = func(progress float64, filesScanned, newItems, errors int) {