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/config/config.go

@@ -20,6 +20,7 @@ type Config struct {
 	Quota         QuotaConfig
 	Internal      InternalConfig
 	SyncOutbox    SyncOutboxConfig
+	TokenRefresh  TokenRefreshConfig
 }
 
 type ServerConfig struct {
@@ -80,6 +81,13 @@ type SyncOutboxConfig struct {
 	MaxRetries      int
 }
 
+type TokenRefreshConfig struct {
+	IntervalSeconds    int
+	RefreshSkewSeconds int
+	BatchSize          int
+	MaxRetries         int
+}
+
 func Load() (*Config, error) {
 	v := viper.New()
 
@@ -111,6 +119,10 @@ func Load() (*Config, error) {
 	v.SetDefault("sync_outbox.interval_seconds", 5)
 	v.SetDefault("sync_outbox.batch_size", 200)
 	v.SetDefault("sync_outbox.max_retries", 10)
+	v.SetDefault("token_refresh.interval_seconds", 1800)
+	v.SetDefault("token_refresh.refresh_skew_seconds", 3000)
+	v.SetDefault("token_refresh.batch_size", 200)
+	v.SetDefault("token_refresh.max_retries", 3)
 
 	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
 	v.AutomaticEnv()
@@ -143,6 +155,10 @@ func Load() (*Config, error) {
 	_ = v.BindEnv("sync_outbox.interval_seconds", "EZ_SYNC_OUTBOX_INTERVAL_SECONDS")
 	_ = v.BindEnv("sync_outbox.batch_size", "EZ_SYNC_OUTBOX_BATCH_SIZE")
 	_ = v.BindEnv("sync_outbox.max_retries", "EZ_SYNC_OUTBOX_MAX_RETRIES")
+	_ = v.BindEnv("token_refresh.interval_seconds", "EZ_TOKEN_REFRESH_INTERVAL_SECONDS")
+	_ = v.BindEnv("token_refresh.refresh_skew_seconds", "EZ_TOKEN_REFRESH_SKEW_SECONDS")
+	_ = v.BindEnv("token_refresh.batch_size", "EZ_TOKEN_REFRESH_BATCH_SIZE")
+	_ = v.BindEnv("token_refresh.max_retries", "EZ_TOKEN_REFRESH_MAX_RETRIES")
 
 	if configFile := os.Getenv("EZ_CONFIG_FILE"); configFile != "" {
 		v.SetConfigFile(configFile)
@@ -208,6 +224,12 @@ func Load() (*Config, error) {
 			BatchSize:       v.GetInt("sync_outbox.batch_size"),
 			MaxRetries:      v.GetInt("sync_outbox.max_retries"),
 		},
+		TokenRefresh: TokenRefreshConfig{
+			IntervalSeconds:    v.GetInt("token_refresh.interval_seconds"),
+			RefreshSkewSeconds: v.GetInt("token_refresh.refresh_skew_seconds"),
+			BatchSize:          v.GetInt("token_refresh.batch_size"),
+			MaxRetries:         v.GetInt("token_refresh.max_retries"),
+		},
 	}
 
 	return cfg, nil