Add support for OAuth-based authentication with access/refresh tokens
and expiration tracking for API keys. Extend provider groups with
static headers configuration and headers profile options.
Changes include:
- Add AccessToken, RefreshToken, ExpiresAt, AccountID, ProjectID to APIKey model
- Add StaticHeaders and HeadersProfile to ProviderGroup model
- Add TokenRefresh configuration for background token management
- Support new provider types: ClaudeCode, Codex, GeminiCLI, Antigravity
- Update sync service to include new fields in provider snapshots
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