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/qwen_login.go

@@ -11,6 +11,12 @@ import (
 )
 
 // DoQwenLogin handles the Qwen device flow using the shared authentication manager.
+// It initiates the device-based authentication process for Qwen services and saves
+// the authentication tokens to the configured auth directory.
+//
+// Parameters:
+//   - cfg: The application configuration
+//   - options: Login options including browser behavior and prompts
 func DoQwenLogin(cfg *config.Config, options *LoginOptions) {
 	if options == nil {
 		options = &LoginOptions{}