build: 改成 Bun workspaces 的 monorepo

- 根目录新增 package.json（workspaces: client、server），两边共用一个 bun.lock，
  依赖版本与原来两个 lockfile 完全一致
- 根目录脚本：bun run dev / build / build:staging / test / typecheck / fmt，
  取代 dev.sh；client 的 start 改名为 dev，包名改为 webpreview-client
- workspaces 用 isolated 安装，补上 client 一直直接 import 却没声明的 @codemirror/view
- server 镜像改用仓库根目录做构建上下文，只装 server 的依赖；
  .dockerignore 用白名单，不再把 node_modules、数据库等发给 docker
- CI 在根目录安装并构建前端

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

client/package.json

@@ -1,10 +1,10 @@
 {
-  "name": "web",
+  "name": "webpreview-client",
   "private": true,
   "version": "0.3.0",
   "type": "module",
   "scripts": {
-    "start": "bun --bun vite",
+    "dev": "bun --bun vite",
     "build": "bun --bun vite build",
     "build:staging": "bun --bun vite build --mode staging",
     "fmt": "bun fmt src/"
@@ -13,6 +13,7 @@
     "@codemirror/lang-css": "^6.3.1",
     "@codemirror/lang-html": "^6.4.12",
     "@codemirror/lang-javascript": "^6.2.5",
+    "@codemirror/view": "^6.41.1",
     "@vueuse/core": "^15.0.0",
     "axios": "^1.20.0",
     "codemirror": "^6.0.2",