feat: Implement core bot logic

- Implements the central orchestrator in `app/main.py` using `python-telegram-bot`.
- Integrates the `permissions` module to determine user roles based on chat IDs.
- Implements the `onboarding` module to provide role-based menus with inline keyboards.
- Adds a `CallbackQueryHandler` to handle button presses from the inline keyboards.
- Updates `tasks.md` to reflect the completion of Phase 2.

app/modules/onboarding.py

@@ -1,9 +1,42 @@
 # app/modules/onboarding.py
+from telegram import InlineKeyboardButton, InlineKeyboardMarkup
 
-def handle_start(chat_id):
+def get_owner_menu():
+    """Returns the main menu for the owner."""
+    keyboard = [
+        [InlineKeyboardButton("📅 Ver mi agenda", callback_data='view_agenda')],
+        [InlineKeyboardButton("⏳ Ver pendientes", callback_data='view_pending')],
+        [InlineKeyboardButton("✅ Aprobar solicitud", callback_data='approve_request')],
+    ]
+    return InlineKeyboardMarkup(keyboard)
+
+def get_team_menu():
+    """Returns the main menu for a team member."""
+    keyboard = [
+        [InlineKeyboardButton("🕒 Proponer actividad", callback_data='propose_activity')],
+        [InlineKeyboardButton("📄 Ver estatus de solicitudes", callback_data='view_requests_status')],
+    ]
+    return InlineKeyboardMarkup(keyboard)
+
+def get_client_menu():
+    """Returns the main menu for a client."""
+    keyboard = [
+        [InlineKeyboardButton("🗓️ Agendar una cita", callback_data='schedule_appointment')],
+        [InlineKeyboardButton("ℹ️ Información de servicios", callback_data='get_service_info')],
+    ]
+    return InlineKeyboardMarkup(keyboard)
+
+def handle_start(user_role):
     """
-    Handles the /start command and sends a welcome message.
+    Handles the /start command and sends a role-based welcome message and menu.
     """
-    print(f"[{chat_id}] Handling start command...")
-    # TODO: Implement welcome message and main menu
-    return "Welcome to Talía!"
+    welcome_message = "Hola, soy Talía. ¿En qué puedo ayudarte hoy?"
+
+    if user_role == "owner":
+        menu = get_owner_menu()
+    elif user_role in ["admin", "team"]:
+        menu = get_team_menu()
+    else: # client
+        menu = get_client_menu()
+
+    return welcome_message, menu