Add comprehensive authentication support for the qBit Manage web UI with multiple methods:
- None (default, no authentication)
- Basic HTTP authentication with browser popup
- API-only authentication (web UI accessible, API requires key)
Key features include:
- Secure password hashing using Argon2
- Rate limiting to prevent brute force attacks
- CSRF protection for state-changing requests
- Local IP bypass option for private networks
- API key generation for programmatic access
- New security settings page in the web UI
Adds [FR]: Authentication on WebUI
Fixes#867
