fix: prevent photo corruption during upload and add batch processing improvements

- Remove async functions from multer callbacks (primary corruption cause)
- Implement temp directory upload approach with proper cleanup
- Add comprehensive file integrity validation before processing
- Fix batch upload category assignment and photo naming
- Add automatic cleanup service for orphaned temp uploads
- Enhance error handling with better corruption detection
- Add fix-temp-photos script to repair existing temporary files
- Update file watcher to ignore temp upload files

Fixes issues with:
- Corrupted photos showing only partial images
- Photos retaining temp_ names after upload
- Category assignments lost during batch uploads
- Incomplete file uploads causing "Premature end of input" errors

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

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

backend/src/services/fileWatcher.js

@@ -51,6 +51,13 @@ async function processNewPhoto(filePath) {
   const ext = path.extname(filePath).toLowerCase();
   if (!['.jpg', '.jpeg', '.png', '.webp'].includes(ext)) return;
   
+  // Skip temporary upload files
+  const filename = path.basename(filePath);
+  if (filename.startsWith('temp_')) {
+    logger.debug(`Skipping temporary upload file: ${filename}`);
+    return;
+  }
+  
   // Find the event
   const event = await db('events').where({ slug: eventSlug, is_active: formatBoolean(true) }).first();
   if (!event) return;