feat: 重写为 GPUI 原生桌面应用并接入 Gitea 软件包发布

- gpui-kit 0.6 原生 UI：连接管理、消息流/日志、发布预设、全局变量、
  设置、阿里云连接预设、原生 Logo
- MQTT 5.0/3.1.1 引擎（rumqttc，TCP/TLS/WS/WSS），独立 tokio runtime
  + 事件泵，真实 broker 端到端测试
- 连接表单：保存前可一键测试连接（宽松校验，自动生成临时 Client ID），
  高级属性（认证/MQTT 5 属性/遗嘱）按需折叠显示，WS 路径仅 WS/WSS 显示
- bug 修复：Hex 奇数长度显式报错、测试连接唯一 Client ID、Base64/Hex
  发布发送真实字节、v5 发布记录携带 Content-Type/用户属性、预设应用
  清除旧 Content-Type、模板时间基准统一；补 8 个单元测试
- Gitea 发布：Generic Package 上传脚本（bash/PowerShell）+ Actions
  release 工作流（tag 触发，双平台构建），README 使用说明

gpui-app/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+name = "mqttx-desktop"
+version = "1.0.0"
+edition.workspace = true
+description = "MQTT X —— 基于 GPUI 的跨平台 MQTT 调试客户端"
+default-run = "mqttx"
+
+[[bin]]
+name = "mqttx"
+path = "src/main.rs"
+
+[dependencies]
+gpui-kit = "0.6"
+
+anyhow = "1"
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+# MQTT 引擎运行在独立的 tokio runtime 线程上
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "sync", "net", "time", "io-util"] }
+# GPUI 侧与引擎线程通信使用 smol 通道（GPUI 执行器兼容）
+smol = "2"
+
+rumqttc = { package = "rumqttc-v5-next", version = "0.34", features = ["websocket"] }
+rumqttc-v4 = { package = "rumqttc-v4-next", version = "0.34", features = ["websocket"] }
+
+uuid = { version = "1", features = ["v4"] }
+chrono = { version = "0.4", features = ["clock"] }
+dirs = "6"
+
+# 阿里云 MQTT 签名: HMAC-SHA1 -> Base64
+hmac = "0.12"
+sha1 = "0.10"
+base64 = "0.22"