Tab selection was being set immediately during app configuration, before
the user account had completed sign-in. This caused tabs that require
authentication (like Subscriptions and Playlists) to not be properly
selected on startup since they weren't visible yet.
Changes:
- Add notification system for account configuration completion
- Post notification after all account types finish configuration:
* Accounts with existing tokens
* Accounts requiring sign-in (after network request completes)
* Anonymous/public accounts
* Error cases (missing credentials, network failures)
- Set up observer before account configuration to ensure notification
is received
- Set tab selection only when account is fully configured
