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>

bot/bot.py

@@ -26,6 +26,7 @@ import ai.parser as ai_parser
 import bot.commands.routines  # noqa: F401 - registers handler
 import bot.commands.medications  # noqa: F401 - registers handler
 import bot.commands.knowledge  # noqa: F401 - registers handler
+import bot.commands.tasks  # noqa: F401 - registers handler
 
 DISCORD_BOT_TOKEN = os.getenv("DISCORD_BOT_TOKEN")
 API_URL = os.getenv("API_URL", "http://app:5000")