重构：Wails v3 迁移 + 前端目录规范化 + Sidebar滚动优化

- web/ → frontend/ 目录重命名（Wails v3 标准结构）
- main.go: Middleware 修复 custom.js 404 + DevTools 延迟启动
- Sidebar: 收藏夹内部独立滚动 + 帮助区块固定底部
- useFavorites.ts: longPressTimer const→let 修复 TypeError
- App.vue: Arco Tabs padding-top 覆盖
- build: config.yml / Taskfile.yml 对齐官方模板，devtools build tag
- 新增 v3 bindings、vite.config.js、跨平台构建配置

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Taskfile.yml

@@ -0,0 +1,60 @@
+version: '3'
+
+includes:
+  common: ./build/Taskfile.yml
+  windows: ./build/windows/Taskfile.yml
+  darwin: ./build/darwin/Taskfile.yml
+  linux: ./build/linux/Taskfile.yml
+  ios: ./build/ios/Taskfile.yml
+  android: ./build/android/Taskfile.yml
+
+vars:
+  APP_NAME: "u-desk"
+  BIN_DIR: "bin"
+  VITE_PORT: '{{.WAILS_VITE_PORT | default 9245}}'
+
+tasks:
+  build:
+    summary: Builds the application
+    cmds:
+      - task: "{{OS}}:build"
+
+  package:
+    summary: Packages a production build of the application
+    cmds:
+      - task: "{{OS}}:package"
+
+  run:
+    summary: Runs the application
+    cmds:
+      - task: "{{OS}}:run"
+
+  dev:
+    summary: Runs the application in development mode
+    cmds:
+      - wails3 dev
+
+  setup:docker:
+    summary: Builds Docker image for cross-compilation (~800MB download)
+    cmds:
+      - task: common:setup:docker
+
+  build:server:
+    summary: Builds the application in server mode (no GUI, HTTP server only)
+    cmds:
+      - task: common:build:server
+
+  run:server:
+    summary: Runs the application in server mode
+    cmds:
+      - task: common:run:server
+
+  build:docker:
+    summary: Builds a Docker image for server mode deployment
+    cmds:
+      - task: common:build:docker
+
+  run:docker:
+    summary: Builds and runs the Docker image
+    cmds:
+      - task: common:run:docker