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.

config.example.yaml

@@ -18,6 +18,9 @@ auth-dir: "~/.cli-proxy-api"
 # Enable debug logging
 debug: false
 
+# When true, write application logs to rotating files instead of stdout
+logging-to-file: true
+
 # Proxy URL. Supports socks5/http/https protocols. Example: socks5://user:pass@192.168.1.1:1080/
 proxy-url: ""