Add cron container and per-household timezone for auto-reminders

- docker-compose.yml: meal-cron service loops send_reminders_cron.py every 60s
- send_reminders_cron.py: checks each household's local time, sends ntfy
  reminders at 10:00 (lunch) and 16:00 (dinner), guarded against duplicates
- models.py: timezone, last_lunch_reminder, last_dinner_reminder on households
- meals.py: /admin/timezone route for admins to set household timezone
- dashboard: timezone selector (20 common zones) in Account Settings
- i18n: 5 new translation keys for timezone strings
- Dockerfile: copy send_reminders_cron.py
- tests: 4 new timezone tests (admin set, non-admin denied, default UTC, auth)
- docs: updated AGENTS.md

docker-compose.yml

@@ -14,6 +14,20 @@ services:
     networks:
       - caddy
 
+  meal-cron:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    command: ["sh", "-c", "while true; do python3 /app/send_reminders_cron.py; sleep 60; done"]
+    volumes:
+      - meal-data:/data
+    environment:
+      - SECRET_KEY=${SECRET_KEY:-change-me-in-production}
+      - APP_BASE_URL=${APP_BASE_URL:-http://meal-tracker:5000}
+    restart: unless-stopped
+    networks:
+      - caddy
+
 volumes:
   meal-data: