chore(docs): add and refine package-level comments across modules

- Added detailed package-level comments to improve documentation coverage.
- Clarified parameter descriptions, return types, and functionality of exported methods across packages.
- Enhanced overall code readability and API documentation consistency.

internal/cmd/auth_manager.go

@@ -4,6 +4,12 @@ import (
 	sdkAuth "github.com/router-for-me/CLIProxyAPI/v6/sdk/auth"
 )
 
+// newAuthManager creates a new authentication manager instance with all supported
+// authenticators and a file-based token store. It initializes authenticators for
+// Gemini, Codex, Claude, and Qwen providers.
+//
+// Returns:
+//   - *sdkAuth.Manager: A configured authentication manager instance
 func newAuthManager() *sdkAuth.Manager {
 	store := sdkAuth.NewFileTokenStore()
 	manager := sdkAuth.NewManager(store,