Add ntfy push notifications with action buttons for meal reminders

- ntfy.py: send_meal_reminder() with Home/Out HTTP action buttons, test helper
- models.py: new columns ntfy_url, ntfy_token, callback_token on users table
- meals.py: /api/ntfy-callback (public, token-authenticated), /ntfy-settings, /ntfy-test
- app.py: flask send-reminders CLI command (cron-schedulable)
- Dashboard: ntfy config form in Account Settings
- i18n: translations for all ntfy strings (en/fr/de)
- Dockerfile: include ntfy.py in COPY
- tests: 15 new tests covering callback, settings, and auth
- docs: updated AGENTS.md and doc/index.md

Dockerfile

@@ -7,7 +7,7 @@ COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 # Copy application
-COPY app.py models.py auth.py meals.py i18n.py ./
+COPY app.py models.py auth.py meals.py i18n.py ntfy.py ./
 COPY templates/ templates/
 COPY static/ static/