feat: Implement Phase 3 modules

- Implements placeholder logic for the `agenda`, `citas`, `equipo`, `aprobaciones`, and `servicios` modules.
- Integrates all new module functions into the `button` handler in `app/main.py` to make the bot's menus functional.
- Fixes a newline formatting bug in the text responses to ensure they render correctly in Telegram.
- Updates `tasks.md` to reflect the progress on Phase 3.

app/modules/agenda.py

@@ -1,9 +1,18 @@
 # app/modules/agenda.py
 
-def get_agenda(chat_id):
+def get_agenda():
     """
-    Fetches and displays the user's agenda.
+    Fetches and displays the user's agenda for today.
+    For now, it returns a hardcoded sample agenda.
     """
-    print(f"[{chat_id}] Fetching agenda...")
-    # TODO: Implement agenda logic
-    return "Here is your agenda for today."
+    # TODO: Fetch agenda from Google Calendar
+    agenda_text = (
+        "📅 *Agenda para Hoy*\n\n"
+        "• *10:00 AM - 11:00 AM*\n"
+        "  Reunión de Sincronización - Proyecto A\n\n"
+        "• *12:30 PM - 1:30 PM*\n"
+        "  Llamada con Cliente B\n\n"
+        "• *4:00 PM - 5:00 PM*\n"
+        "  Bloque de trabajo profundo - Desarrollo Talía"
+    )
+    return agenda_text