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/package.json

@@ -1,6 +1,6 @@
 {
   "name": "picpeak-backend",
-  "version": "1.0.62",
+  "version": "1.0.63",
   "description": "Backend for PicPeak event photo sharing platform",
   "main": "server.js",
   "scripts": {
@@ -8,6 +8,7 @@
     "dev": "nodemon server.js",
     "migrate": "node migrations/run-migrations.js",
     "migrate:safe": "node migrations/run-migrations-safe.js",
+    "fix-temp-photos": "node scripts/fix-temp-photos.js",
     "test": "jest",
     "lint": "eslint src/"
   },