fix: photo upload issues with file limit and date formatting

- Add 20-file limit validation to PhotoUpload component
- Prevent Multer "Unexpected field" errors by enforcing client-side limit
- Fix JSON parsing error in dateFormatter when value is already an object
- Add missing translation keys for upload error messages
- Handle both string and object values for date format settings

These fixes resolve the 400 error when uploading more than 20 files
and the "Unexpected token o in JSON" error during email queue creation.

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

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

frontend/src/i18n/locales/en.json

@@ -47,7 +47,10 @@
     "uploadComplete": "Upload complete!",
     "uploadFailed": "Upload failed",
     "someFilesFailed": "Some files failed to upload",
-    "uploadPhotos": "Upload Photos"
+    "uploadPhotos": "Upload Photos",
+    "maxFilesReached": "Maximum 20 files allowed",
+    "someFilesSkipped": "Some files were skipped (20 file limit)",
+    "tooManyFiles": "Maximum 20 files can be uploaded at once"
   },
   "navigation": {
     "dashboard": "Dashboard",