feat: 添加完整的前端管理系统 (VbenAdmin)

- 添加基于 VbenAdmin + Vue3 + Element Plus 的前端管理系统
- 包含完整的 UI 组件库和工具链
- 支持多应用架构 (web-ele, backend-mock, playground)
- 包含完整的开发规范和配置
- 修复 admin 目录的子模块问题，确保正确提交

admin/.github/workflows/lock.yml

@@ -0,0 +1,24 @@
+name: Lock Threads
+
+on:
+  schedule:
+    - cron: '0 0 * * *'
+  workflow_dispatch:
+
+permissions:
+  issues: write
+  pull-requests: write
+
+jobs:
+  action:
+    if: github.repository == 'vbenjs/vue-vben-admin'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@v5
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          issue-inactive-days: '14'
+          issue-lock-reason: ''
+          pr-inactive-days: '30'
+          pr-lock-reason: ''
+          process-only: 'issues, prs'