dsh-message-gateway: Multi-Platform Message Gateway for DSH Web

`dsh-message-gateway` is a plugin for DSH Web GUI designed to manage multi-platform messages in a unified manner. Integrated into the sidebar, it supports connections to more than ten platforms, including Telegram, Discord, and WeCom, and provides endpoints for streaming responses and proactive push notifications. The plugin features plaintext credential storage on disk, sensitive information redaction, inbound Webhook handling, and multilingual support. It is easy to install and suitable for developers building cross-platform message routing and automated notification scenarios.