Fix Firebase authentication error and improve credential handling

[sohampirale]

Issue Description

• The application fails to start with TypeError: initialize_app() got an unexpected keyword argument 'credentials' due to incorrect Firebase initialization syntax and hardcoded credential path.

Issue Details

 - Current code uses invalid parameter name credentials= in firebase_admin.initialize_app()
 - Credential file path is hardcoded instead of configurable
 - Not following production best practices for credential management