feat: initial MQTT v5 debugging tool

- Tauri v2 + Vue 3 + TypeScript + Element Plus
- Connection management (CRUD + enable/disable/test)
- Preset system with {{variable}} placeholders
- Dashboard with live message scrolling + topic tree
- Payload inspector (JSON/Hex/Base64/Plain)
- Protocol-level logging (file + UI dual channel)
- Global variable manager with localStorage persistence
- MQTT v5 property support (user properties, content type, etc.)
- SubAck result tracking with subscribe_tracked API

README.md

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+# Tauri + Vue + TypeScript
+
+This template should help get you started developing with Vue 3 and TypeScript in Vite. The template uses Vue 3 `<script setup>` SFCs, check out the [script setup docs](https://v3.vuejs.org/api/sfc-script-setup.html#sfc-script-setup) to learn more.
+
+## Recommended IDE Setup
+
+- [VS Code](https://code.visualstudio.com/) + [Vue - Official](https://marketplace.visualstudio.com/items?itemName=Vue.volar) + [Tauri](https://marketplace.visualstudio.com/items?itemName=tauri-apps.tauri-vscode) + [rust-analyzer](https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer)
+
+
+
+Template created! To get started run:
+  `cd mqttx`
+  `pnpm install`
+  <!-- pnpm tauri android init -->
+
+For Desktop development, run:
+  `pnpm tauri dev`
+
+For Android development, run:
+  <!-- pnpm tauri android dev -->