feat: Implement core application structure, AI extraction, persistence, and Telegram bot modules with updated configuration and dependencies.

app/permissions.py

@@ -0,0 +1,20 @@
+"""
+Handles user permissions and access control.
+
+Defines who is allowed to perform certain actions, such as uploading
+or querying expense data.
+"""
+
+from app.config import config
+
+def is_user_allowed(user_id: str) -> bool:
+    """
+    Checks if a given user ID is allowed to use the bot.
+
+    For now, this is a stub. A real implementation could check against
+    a database of users or a predefined list in the config.
+    """
+    # For example, you could have a comma-separated list of allowed IDs
+    # ALLOWED_USERS = config.ALLOWED_USER_IDS.split(',')
+    # return user_id in ALLOWED_USERS
+    return True # Allow all users for now