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/middleware/uploadValidation.js

@@ -20,10 +20,19 @@ async function validateUploadedFile(filePath) {
     
     if (imageExtensions.includes(ext)) {
       // Try to read metadata - this will fail if image is corrupted
-      const metadata = await sharp(filePath).metadata();
+      let metadata;
+      try {
+        metadata = await sharp(filePath, {
+          failOnError: false, // Don't fail on recoverable errors
+          limitInputPixels: 268402689 // ~16k x 16k max
+        }).metadata();
+      } catch (metadataError) {
+        // If metadata reading fails, the file is likely incomplete
+        throw new Error(`Invalid image file: ${metadataError.message}`);
+      }
       
-      if (!metadata.width || !metadata.height) {
-        throw new Error('Invalid image dimensions');
+      if (!metadata || !metadata.width || !metadata.height) {
+        throw new Error('Invalid image dimensions - file may be incomplete');
       }
       
       // Check for reasonable dimensions
@@ -31,6 +40,18 @@ async function validateUploadedFile(filePath) {
         throw new Error('Image dimensions too small');
       }
       
+      // Additional check: verify we can actually decode a small portion of the image
+      try {
+        await sharp(filePath, {
+          failOnError: false,
+          limitInputPixels: 268402689
+        })
+        .resize(10, 10) // Try to resize to very small size
+        .toBuffer();
+      } catch (decodeError) {
+        throw new Error(`Image decode failed - file may be corrupted: ${decodeError.message}`);
+      }
+      
       return true;
     }