refactor(config): migrate to SDKConfig and streamline proxy handling

- Replaced `config.Config` with `config.SDKConfig` across components for simpler configuration management.
- Updated proxy setup functions and handlers to align with `SDKConfig` improvements.
- Reorganized handler imports to match new SDK structure.

internal/auth/codex/openai_auth.go

@@ -37,7 +37,7 @@ type CodexAuth struct {
 // It initializes an HTTP client with proxy settings from the provided configuration.
 func NewCodexAuth(cfg *config.Config) *CodexAuth {
 	return &CodexAuth{
-		httpClient: util.SetProxy(cfg, &http.Client{}),
+		httpClient: util.SetProxy(&cfg.SDKConfig, &http.Client{}),
 	}
 }