feat(api): add OAuth token fields and new provider types support

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

internal/dto/provider_group.go

@@ -7,6 +7,8 @@ type ProviderGroupDTO struct {
 	BaseURL        string   `json:"base_url"`
 	GoogleProject  string   `json:"google_project,omitempty"`
 	GoogleLocation string   `json:"google_location,omitempty"`
+	StaticHeaders  string   `json:"static_headers,omitempty"`
+	HeadersProfile string   `json:"headers_profile,omitempty"`
 	Models         []string `json:"models"`
 	Status         string   `json:"status"`
 }