feat: add update instructions dialog, email notifications, and capture date sorting

- Add Update Instructions Dialog with environment-specific commands (Docker/Git/Standalone)
- Add email notification settings for new version alerts
- Add "Sort by Capture Date" option using EXIF metadata extraction
- Fix E2E tests by loading environment variables via dotenv
- Add test-images/ and backend/*.db to .gitignore

Closes #181

.gitignore

@@ -102,8 +102,10 @@ backup/
 
 # Local SQLite files in backend
 backend/*.sqlite*
+backend/*.db
 
 # Test files and artifacts
+test-images/
 test-logo*.jpg
 test-logo*.png
 test-results/