feat(collections,media): add bulk operations for books and collections

Collections:
- HandleBulkAddBooks: add multiple books to multiple collections

Media:
- HandleBulkDelete: delete multiple media items
- HandleBulkUpdate: bulk update book metadata (tags, status)
- Individual result tracking for each operation
- WebSocket broadcasts for collection updates

internal/handlers/collections.go

@@ -715,3 +715,102 @@ func (h *CollectionHandler) compareValues(itemValue, operator, ruleValue string)
 	}
 	return false
 }
+
+// Bulk Operations
+
+// POST /api/collections/bulk-add-books
+// Bulk add books to multiple collections
+func (h *CollectionHandler) HandleBulkAddBooks(c echo.Context) error {
+	user := c.Get("user").(database.Users)
+
+	var req struct {
+		Operations []struct {
+			CollectionID string   `json:"collection_id" validate:"required"`
+			BookIDs      []string `json:"book_ids" validate:"required"`
+		} `json:"operations" validate:"required"`
+	}
+
+	if err := c.Bind(&req); err != nil {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "Invalid request"})
+	}
+
+	if len(req.Operations) == 0 {
+		return c.JSON(http.StatusBadRequest, map[string]string{"error": "operations required"})
+	}
+
+	results := make([]map[string]interface{}, 0)
+	successCount := 0
+	failedCount := 0
+
+	for _, op := range req.Operations {
+		collectionID, err := uuid.Parse(op.CollectionID)
+		if err != nil {
+			results = append(results, map[string]interface{}{
+				"collection_id": op.CollectionID,
+				"status":        "error",
+				"error":         "Invalid collection UUID",
+			})
+			failedCount++
+			continue
+		}
+
+		for _, bookIDStr := range op.BookIDs {
+			bookID, err := uuid.Parse(bookIDStr)
+			if err != nil {
+				results = append(results, map[string]interface{}{
+					"collection_id": op.CollectionID,
+					"book_id":       bookIDStr,
+					"status":        "error",
+					"error":         "Invalid book UUID",
+				})
+				failedCount++
+				continue
+			}
+
+			collectionUUID := pgtype.UUID{Bytes: collectionID, Valid: true}
+			bookUUID := pgtype.UUID{Bytes: bookID, Valid: true}
+
+			_, err = h.db.AddBookToCollection(c.Request().Context(), database.AddBookToCollectionParams{
+				CollectionID:  collectionUUID,
+				MediaItemID:   bookUUID,
+				AddedByUserID: pgtype.UUID{Bytes: user.ID.Bytes, Valid: true},
+			})
+
+			if err != nil {
+				results = append(results, map[string]interface{}{
+					"collection_id": op.CollectionID,
+					"book_id":       bookIDStr,
+					"status":        "error",
+					"error":         err.Error(),
+				})
+				failedCount++
+				continue
+			}
+
+			results = append(results, map[string]interface{}{
+				"collection_id": op.CollectionID,
+				"book_id":       bookIDStr,
+				"status":        "success",
+			})
+			successCount++
+		}
+	}
+
+	if successCount > 0 && h.connManager != nil {
+		h.connManager.Broadcast(wsync.BroadcastMessage{
+			Type:      "collection_updated",
+			Timestamp: time.Now().Format(time.RFC3339),
+			Data: map[string]interface{}{
+				"action": "books_added_bulk",
+				"count":  successCount,
+			},
+		})
+	}
+
+	return c.JSON(http.StatusOK, map[string]interface{}{
+		"results": results,
+		"total":   len(results),
+		"success": successCount,
+		"failed":  failedCount,
+	})
+}