- Settings: add date_format and time_format (model, migration 119, admin UI)
- Use user date/time prefs in templates, calendar, and PDF export
- Expense: eager-load client instead of category in repo, service, and API
- Mobile: clarify server URL and certificate docs, bump to 4.18.0, improve connection diagnostics
- Ignore mobile/android/.gradle/
Co-authored-by: Cursor <cursoragent@cursor.com>