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/main.py

@@ -1,10 +1,53 @@
 # app/main.py
+import logging
+from telegram import Update
+from telegram.ext import Application, CommandHandler, CallbackQueryHandler, ContextTypes
 
-def main():
-    """
-    Main function to run the bot.
-    """
-    print("Talía Bot is running...")
+from config import TELEGRAM_BOT_TOKEN
+from permissions import get_user_role
+from modules.onboarding import handle_start as onboarding_handle_start
+
+# Enable logging
+logging.basicConfig(
+    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s", level=logging.INFO
+)
+logger = logging.getLogger(__name__)
+
+async def start(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
+    """Sends a welcome message and menu when the /start command is issued."""
+    chat_id = update.effective_chat.id
+    user_role = get_user_role(chat_id)
+
+    logger.info(f"User {chat_id} started conversation with role: {user_role}")
+
+    # Delegate to the onboarding module
+    response_text, reply_markup = onboarding_handle_start(user_role)
+
+    await update.message.reply_text(response_text, reply_markup=reply_markup)
+
+async def button(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
+    """Parses the CallbackQuery and updates the message text."""
+    query = update.callback_query
+    await query.answer()
+    # TODO: Implement handlers for the different callback queries
+    await query.edit_message_text(text=f"Selected option: {query.data}")
+
+def main() -> None:
+    """Start the bot."""
+    if not TELEGRAM_BOT_TOKEN:
+        logger.error("TELEGRAM_BOT_TOKEN is not set in the environment variables.")
+        return
+
+    # Create the Application and pass it your bot's token.
+    application = Application.builder().token(TELEGRAM_BOT_TOKEN).build()
+
+    # Add command handlers
+    application.add_handler(CommandHandler("start", start))
+    application.add_handler(CallbackQueryHandler(button))
+
+    # Run the bot until the user presses Ctrl-C
+    logger.info("Starting Talía Bot...")
+    application.run_polling()
 
 if __name__ == "__main__":
     main()