Create CLI auth commands

[Hozyne-OpenBak]

Part of #2

Build CLI for authentication management.

Commands:

• infershield auth login [provider] - Initiate device flow
• infershield auth logout [provider] - Revoke tokens
• infershield auth status - Show authenticated providers
• infershield auth list - List all stored tokens

UX:

$ infershield auth login openai
Visit: https://github.com/login/device
Enter code: ABCD-1234
Waiting for authorization...
✓ Authenticated as alex@example.com