docs: Add production deployment notes for file uploads issue

- Document the 404 error for uploaded images
- Explain that uploads directory needs to persist in production
- Provide solutions: persistent directory or cloud storage
- Add debug endpoint suggestion to check upload directory

PRODUCTION_DEPLOYMENT_NOTES.md

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+# Production Deployment Notes
+
+## File Uploads Issue
+
+### Problem
+Images are returning 404 errors in production because the uploads directory is not persisting or is in the wrong location.
+
+### Current Configuration
+- Backend serves uploads from: `/uploads` route
+- Files are stored in: `UPLOAD_DIR` environment variable (default: `./uploads`)
+- File URLs in database: `/uploads/photo-{timestamp}-{random}.jpeg`
+
+### Solution Options
+
+#### Option 1: Ensure Persistent Upload Directory (Recommended)
+Make sure the uploads directory on the production server persists across deployments:
+
+```bash
+# On production server
+cd /path/to/server
+mkdir -p uploads
+chmod 755 uploads
+
+# Set in .env
+UPLOAD_DIR=/absolute/path/to/uploads
+```
+
+#### Option 2: Use Cloud Storage (Better for Production)
+Instead of local file storage, use cloud storage like AWS S3, Cloudinary, or similar:
+
+1. Update `server/src/middleware/upload.ts` to use cloud storage
+2. Update photo URLs to point to cloud storage
+3. No need for local uploads directory
+
+### Checking Upload Directory
+
+Add this to your server to debug:
+
+```typescript
+// In server/src/index.ts
+app.get('/debug/uploads', (req, res) => {
+  const uploadDir = process.env.UPLOAD_DIR || path.join(process.cwd(), 'uploads');
+  const fs = require('fs');
+  
+  res.json({
+    uploadDir,
+    exists: fs.existsSync(uploadDir),
+    files: fs.existsSync(uploadDir) ? fs.readdirSync(uploadDir) : [],
+    cwd: process.cwd(),
+  });
+});
+```
+
+### Current Status
+- ✅ Frontend correctly requests: `https://litter-api.psbailey.uk/uploads/photo-xxx.jpeg`
+- ✅ Backend serves uploads from `/uploads` route
+- ❌ Files don't exist in the uploads directory on production server
+
+### Action Required
+1. Check if uploads directory exists on production server
+2. Verify UPLOAD_DIR environment variable is set correctly
+3. Ensure uploads directory has correct permissions
+4. Consider implementing cloud storage for production