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

build-linux-docker.ps1

@@ -0,0 +1,19 @@
+Write-Host "===== Web2App Linux Docker Build ====="
+Write-Host ""
+Write-Host "This script builds the Linux version using Docker."
+Write-Host "Prerequisites: Docker Desktop with Linux container support"
+Write-Host ""
+
+$imageName = "web2app-linux-builder"
+
+Write-Host "1. Building Docker image..."
+docker build -t $imageName .
+
+Write-Host "2. Running build..."
+$outputDir = Join-Path (Get-Location) "release-linux"
+New-Item -ItemType Directory -Force -Path $outputDir
+docker run --rm -v "${outputDir}:/output" $imageName
+
+Write-Host ""
+Write-Host "===== Build Complete ====="
+Write-Host "Output: $outputDir"