fix: improve email processor reliability and add diagnostic tools

- Enhanced email processor with comprehensive logging
- Added error handling for database queries in email processing
- Fixed duplicate export in module.exports
- Added testEmailConnection() function for connectivity testing
- Created diagnostic scripts:
  - check-email-processor.js: Full diagnostic with manual processing
  - run-email-processor.js: Standalone processor (can run once or continuously)
  - check-email-environment.js: Environment and configuration checker
- Fixed missing translation: added 'common.unknown' in EN/DE locales

This should help identify why emails aren't being processed on production.

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

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

frontend/src/i18n/locales/de.json

@@ -34,7 +34,8 @@
     "upload": "Hochladen",
     "days": "Tage",
     "customize": "Anpassen",
-    "hide": "Ausblenden"
+    "hide": "Ausblenden",
+    "unknown": "Unbekannt"
   },
   "upload": {
     "photoCategory": "Fotokategorie",

frontend/src/i18n/locales/en.json

@@ -34,7 +34,8 @@
     "upload": "Upload",
     "days": "days",
     "customize": "Customize",
-    "hide": "Hide"
+    "hide": "Hide",
+    "unknown": "Unknown"
   },
   "upload": {
     "photoCategory": "Photo Category",