feat(logging): introduce centralized logging with custom format and Gin integration

- Implemented a global logger with structured formatting for consistent log output.
- Added support for rotating log files using Lumberjack.
- Integrated new logging functionality with Gin HTTP server for unified log handling.
- Replaced direct `log.Info` calls with `fmt.Printf` in non-critical paths to simplify core functionality.

internal/cmd/login.go

@@ -62,8 +62,8 @@ func DoLogin(cfg *config.Config, projectID string, options *LoginOptions) {
 	}
 
 	if savedPath != "" {
-		log.Infof("Authentication saved to %s", savedPath)
+		fmt.Printf("Authentication saved to %s\n", savedPath)
 	}
 
-	log.Info("Gemini authentication successful!")
+	fmt.Println("Gemini authentication successful!")
 }