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/media_scanner_settings_test.go

@@ -0,0 +1,26 @@
+package services
+
+import (
+	"testing"
+	"time"
+)
+
+func TestMediaScanner_GetPollInterval(t *testing.T) {
+	t.Run("nil db returns default", func(t *testing.T) {
+		scanner := &MediaScanner{db: nil}
+		interval := scanner.GetPollInterval()
+		if interval != 30*time.Second {
+			t.Errorf("expected 30s, got %v", interval)
+		}
+	})
+}
+
+func TestMediaScanner_GetAutoScanEnabled(t *testing.T) {
+	t.Run("nil db returns default true", func(t *testing.T) {
+		scanner := &MediaScanner{db: nil}
+		enabled := scanner.GetAutoScanEnabled()
+		if enabled != true {
+			t.Errorf("expected true, got %v", enabled)
+		}
+	})
+}