feat: Implement LLM and scheduler functionalities

This commit finalizes Phase 4 of the project by implementing the
LLM and scheduler integrations.

- Implements `get_smart_response` in `app/llm.py` to generate
  AI-powered responses using the OpenAI API.
- Implements a daily summary scheduler in `app/scheduler.py` using
  the `JobQueue` from `python-telegram-bot` for better integration
  with the application's event loop.
- Adds `get_events_for_day` to `app/calendar.py` to fetch daily
  events for the summary.
- Integrates the scheduler into the main application loop in
  `app/main.py`.
- Improves the date formatting in the daily summary for better
  readability.
- Updates `tasks.md` to reflect the completion of Phase 4.

app/scheduler.py

@@ -1,27 +1,52 @@
 # app/scheduler.py
 
-import schedule
-import time
-from datetime import datetime
+import datetime
+import pytz
+from telegram import Bot
+from app.config import OWNER_CHAT_ID, TIMEZONE
+from app.calendar import get_events_for_day
 
-from config import TIMEZONE
 
-def send_daily_summary():
+def format_event_time(start_time_str):
+    """
+    Formats the event start time into a user-friendly format.
+    """
+    if "T" in start_time_str:  # It's a dateTime
+        dt_object = datetime.datetime.fromisoformat(start_time_str)
+        return dt_object.strftime("%I:%M %p")
+    else:  # It's a date
+        return "All day"
+
+
+async def send_daily_summary(context):
     """
     Sends the daily summary to the owner.
     """
-    print(f"[{datetime.now()}] Sending daily summary...")
-    # TODO: Implement the logic to fetch and send the summary
+    bot = context.bot
+    today = datetime.datetime.now(pytz.timezone(TIMEZONE)).date()
+    events = get_events_for_day(today)
 
-def main():
+    if not events:
+        summary = "Good morning! You have no events scheduled for today."
+    else:
+        summary = "Good morning! Here is your schedule for today:\n\n"
+        for event in events:
+            start = event["start"].get("dateTime", event["start"].get("date"))
+            formatted_time = format_event_time(start)
+            summary += f"- {event['summary']} at {formatted_time}\n"
+
+    await bot.send_message(chat_id=OWNER_CHAT_ID, text=summary)
+
+
+def setup_scheduler(application):
     """
-    Main function to run the scheduler.
+    Sets up the daily summary job.
     """
-    schedule.every().day.at("07:00").do(send_daily_summary)
-
-    while True:
-        schedule.run_pending()
-        time.sleep(1)
-
-if __name__ == "__main__":
-    main()
+    tz = pytz.timezone(TIMEZONE)
+    job_queue = application.job_queue
+    job_queue.run_daily(
+        send_daily_summary,
+        time=datetime.time(hour=7, minute=0, tzinfo=tz),
+        chat_id=OWNER_CHAT_ID,
+        name="daily_summary",
+    )