chore: 激活验证闭环 — pre-commit hook + CI gate + npm test scripts

三层质量保障闭环：

package.json:
- 新增 typecheck / test:unit / test:smoke / test:e2e / test / prepare 脚本
- 新增 lint-staged 配置（仅对暂存 .ts/.tsx 文件运行 eslint --fix）
- 新增 devDependencies: husky, lint-staged, tsx

.husky/pre-commit:
- 依次执行 lint-staged → tsc --noEmit → 单元测试
- 任一步骤失败即阻止提交

src/__tests__/e2e/smoke.spec.ts:
- 5 个 Playwright @smoke 测试覆盖核心路由 (/, /chat, /plugins, /plugins/mcp, /settings)
- 检查 HTTP 状态、Next.js 错误覆盖层、标题、console 错误
- 复用已有 helpers (goToChat, goToPlugins, goToMCP, goToSettings, collectConsoleErrors, filterCriticalErrors)

.github/workflows/build.yml:
- 新增 lint-test job (ubuntu-latest): lint → typecheck → unit tests
- 新增 pull_request 触发器
- 三个 build job 添加 needs: [lint-test]，lint-test 失败则不构建
- lint 步骤暂设 continue-on-error（存量 4 个 lint error 待修复）

CLAUDE.md:
- 新增"自检命令"区块，说明 test / test:smoke / test:e2e 用途

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -13,6 +13,8 @@ on:
           - windows
           - macos
           - linux
+  pull_request:
+    branches: [main]
   push:
     tags:
       - "v*"
@@ -21,7 +23,32 @@ permissions:
   contents: write
 
 jobs:
+  lint-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        # TODO: fix 4 existing lint errors then remove continue-on-error
+        continue-on-error: true
+        run: npm run lint
+
+      - name: Typecheck
+        run: npm run typecheck
+
+      - name: Unit tests
+        run: npm run test:unit
+
   build-windows:
+    needs: [lint-test]
     if: ${{ github.event_name == 'push' || inputs.platform == 'all' || inputs.platform == 'windows' }}
     runs-on: windows-latest
     steps:
@@ -50,6 +77,7 @@ jobs:
           retention-days: 3
 
   build-macos:
+    needs: [lint-test]
     if: ${{ github.event_name == 'push' || inputs.platform == 'all' || inputs.platform == 'macos' }}
     runs-on: macos-latest
     env:
@@ -132,6 +160,7 @@ jobs:
           retention-days: 3
 
   build-linux:
+    needs: [lint-test]
     if: ${{ github.event_name == 'push' || inputs.platform == 'all' || inputs.platform == 'linux' }}
     runs-on: ubuntu-latest
     strategy: