Add multi-image support for task completions and documents

- Add TaskCompletionImage and DocumentImage models with one-to-many relationships
- Update admin panel to display images for completions and documents
- Add image arrays to API request/response DTOs
- Update repositories with Preload("Images") for eager loading
- Fix seed SQL execution to use raw SQL instead of prepared statements
- Fix table names in seed file (admin_users, push_notifications_*)
- Add comprehensive seed test data with 34 completion images and 24 document images
- Add subscription limitations admin feature with toggle
- Update admin sidebar with limitations link

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/handlers/task_handler.go

@@ -419,7 +419,7 @@ func (h *TaskHandler) CreateCompletion(c *gin.Context) {
 					c.JSON(http.StatusBadRequest, gin.H{"error": "failed to upload image: " + err.Error()})
 					return
 				}
-				req.PhotoURL = result.URL
+				req.ImageURLs = append(req.ImageURLs, result.URL)
 			}
 		}
 	} else {