feat: 添加跨平台打包支持（Linux .deb）、Docker 构建脚本及项目官网

- electron/builder.js: 修复 Linux 平台 npm 命令、增加 .deb 安装包支持
- electron/main.js: 按平台动态设置保存对话框默认扩展名
- package.json: 添加 Linux deb 打包目标
- 新增 Dockerfile 用于 Linux 交叉构建
- 新增 build-linux-docker.ps1 / build-linux.sh 构建脚本
- 新增 site/ 项目官网页面
- .gitignore: 全面忽略二进制文件
- 新增 GitHub Actions CI 工作流

.github/workflows/build.yml

@@ -0,0 +1,58 @@
+name: Build Web2App
+
+on:
+  push:
+    tags:
+      - 'v*'
+  workflow_dispatch:
+
+jobs:
+  build-windows:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+      - run: npm ci
+      - run: npm run build
+      - run: npx electron-builder --config --win
+      - uses: actions/upload-artifact@v4
+        with:
+          name: Web2App-Windows
+          path: release/*.exe
+
+  build-macos:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+      - run: npm ci
+      - run: npm run build
+      - run: npx electron-builder --config --mac
+      - uses: actions/upload-artifact@v4
+        with:
+          name: Web2App-macOS
+          path: release/*.dmg
+
+  build-linux:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+      - run: |
+          sudo apt-get update
+          sudo apt-get install -y rpm libx11-dev libxkbfile-dev libsecret-1-dev
+      - run: npm ci
+      - run: npm run build
+      - run: npx electron-builder --config --linux
+      - uses: actions/upload-artifact@v4
+        with:
+          name: Web2App-Linux
+          path: |
+            release/*.AppImage
+            release/*.deb