Implement three authentication methods for Confluence, ServiceNow, and Azure DevOps:
1. **OAuth2** - Traditional OAuth flow for enterprise SSO environments
2. **Embedded Browser** - Webview-based login that captures session cookies/tokens
- Solves VPN constraints: users authenticate off-VPN via web UI
- Extracted credentials work on-VPN for API calls
- Based on confluence-publisher agent pattern
3. **Manual Token** - Direct API token/PAT input as fallback
**Changes:**
- Add webview_auth.rs module for embedded browser authentication
- Implement authenticate_with_webview and extract_cookies_from_webview commands
- Implement save_manual_token command with validation
- Add AuthMethod enum to support all three modes
- Add RadioGroup UI component for mode selection
- Complete rewrite of Integrations settings page with mode-specific UI
- Add secondary button variant for UI consistency
**VPN-friendly design:**
Users can authenticate via webview when off-VPN (web UI accessible), then use extracted cookies for API calls when on-VPN (API requires VPN). Addresses enterprise SSO limitations where OAuth app registration is blocked.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
