feat: 初始化 Halo 暗色模式插件

- Halo Plugin 后端（Java/Gradle），含 DarkModePlugin 主类和测试
- Vue 3 + TypeScript 前端 UI，包含主题切换组件和设置页面
- 暗色模式 CSS 变量和覆盖样式（布局/编辑器/表单/滚动条等）
- 设计文档和调查文档
- Halo 插件/主题开发 Agent Skills

Co-Authored-By: Claude <noreply@anthropic.com>

.agents/skills/halo-theme-dev/assets/theme-vite/package.json

@@ -0,0 +1,14 @@
+{
+  "type": "module",
+  "scripts": {
+    "dev": "vite build --watch",
+    "build": "vite build && theme-package",
+    "build-only": "vite build"
+  },
+  "devDependencies": {
+    "@halo-dev/theme-package-cli": "^1.0.1",
+    "@halo-dev/vite-plugin-halo-theme": "1.0.3",
+    "vite": "^8.0.0"
+  },
+  "packageManager": "pnpm@10.33.0"
+}