Add folder validation to CreateMediaItem handler

- Check library has folders before creating media items
- Return HTTP 400 with clear error message if no folders
- Proper error code (400) instead of generic 500
- Improved user feedback for invalid operations
- Inject LibraryService into MediaHandler

Fixes: TestCollectionsBulkOperations HTTP 500 errors
Related: Service layer validation commit

internal/handlers/media.go

@@ -84,13 +84,15 @@ type UpdateMediaHighlightRequest struct {
 }
 
 type MediaHandler struct {
-	db     *database.Queries
-	worker *services.Worker
+	db             *database.Queries
+	worker         *services.Worker
+	libraryService *services.LibraryService
 }
 
-func NewMediaHandler(db *database.Queries, worker ...*services.Worker) *MediaHandler {
+func NewMediaHandler(db *database.Queries, libraryService *services.LibraryService, worker ...*services.Worker) *MediaHandler {
 	mh := &MediaHandler{
-		db: db,
+		db:             db,
+		libraryService: libraryService,
 	}
 	if len(worker) > 0 && worker[0] != nil {
 		mh.worker = worker[0]
@@ -913,6 +915,17 @@ func (mh *MediaHandler) CreateMediaItem(c echo.Context) error {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
 	}
 
+	// Validate library has folders before allowing media items
+	hasFolders, err := mh.libraryService.HasFolders(c.Request().Context(), pgtype.UUID{Bytes: req.LibraryID, Valid: true})
+	if err != nil {
+		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "Failed to validate library folders"})
+	}
+	if !hasFolders {
+		return c.JSON(http.StatusBadRequest, map[string]string{
+			"error": "Cannot add media items to a library with no folders. Please add at least one folder to the library first.",
+		})
+	}
+
 	mediaItemID, err := mh.db.CreateMediaItem(c.Request().Context(), database.CreateMediaItemParams{
 		LibraryID:          pgtype.UUID{Bytes: req.LibraryID, Valid: true},
 		Title:              req.Title,