Add one-off tasks/appointments feature

- DB: tasks table with scheduled_datetime, reminder_minutes_before, advance_notified, status
- API: CRUD routes GET/POST /api/tasks, PATCH/DELETE /api/tasks/<id>
- Scheduler: check_task_reminders() fires advance + at-time notifications, tracks advance_notified to prevent double-fire
- Bot: handle_task() with add/list/done/cancel/delete actions + datetime resolution helper
- AI: task interaction type + examples added to command_parser
- Web: task list page with overdue/notified color coding + new task form with datetime-local picker
- Nav: replaced Templates with Tasks in bottom nav

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/main.py

@@ -24,6 +24,7 @@ import api.routes.victories as victories_routes
 import api.routes.adaptive_meds as adaptive_meds_routes
 import api.routes.snitch as snitch_routes
 import api.routes.ai as ai_routes
+import api.routes.tasks as tasks_routes
 
 app = flask.Flask(__name__)
 CORS(app)
@@ -43,6 +44,7 @@ ROUTE_MODULES = [
     adaptive_meds_routes,
     snitch_routes,
     ai_routes,
+    tasks_routes,
 ]