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

meals.py

@@ -25,6 +25,8 @@ from models import (
     set_user_ntfy,
     get_user_ntfy,
     get_user_by_callback_token,
+    set_household_timezone,
+    get_household_by_id,
 )
 from i18n import t
 from ntfy import send_test_notification
@@ -73,6 +75,7 @@ def dashboard():
 
     data = get_dashboard_data(today, household_id)
     ntfy = get_user_ntfy(session["user_id"])
+    household = get_household_by_id(household_id)
     return render_template(
         "dashboard.html",
         dashboard=data,
@@ -83,6 +86,7 @@ def dashboard():
         current_user_id=session["user_id"],
         is_admin=session["is_admin"],
         ntfy=ntfy,
+        household=household,
     )
 
 
@@ -132,6 +136,7 @@ def history():
 
     data = get_dashboard_data(target_date, session["household_id"])
     ntfy = get_user_ntfy(session["user_id"])
+    household = get_household_by_id(session["household_id"])
     return render_template(
         "dashboard.html",
         dashboard=data,
@@ -143,6 +148,7 @@ def history():
         is_admin=session["is_admin"],
         history_mode=True,
         ntfy=ntfy,
+        household=household,
     )
 
 
@@ -221,6 +227,24 @@ def admin_delete_household():
     return redirect(url_for("auth.login"))
 
 
+@meals_bp.route("/admin/timezone", methods=["POST"])
+@login_required
+def admin_set_timezone():
+    """Admin sets the household timezone."""
+    if not session["is_admin"]:
+        flash(t("Only admins can change the timezone."), "error")
+        return redirect(url_for("meals.dashboard"))
+
+    timezone = request.form.get("timezone", "").strip()
+    if not timezone:
+        flash(t("Please select a timezone."), "error")
+        return redirect(url_for("meals.dashboard"))
+
+    set_household_timezone(session["household_id"], timezone)
+    flash(t("Timezone updated."), "success")
+    return redirect(url_for("meals.dashboard"))
+
+
 # ── Ntfy integration ─────────────────────────────────────────────────────────
 
 @meals_bp.route("/ntfy-settings", methods=["POST"])