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/rerun.yml

@@ -0,0 +1,19 @@
+name: Rerun workflow
+
+on:
+  workflow_dispatch:
+    inputs:
+      run_id:
+        description: The workflow id to relanch
+        required: true
+jobs:
+  rerun:
+    runs-on: ubuntu-latest
+    steps:
+      - name: rerun ${{ inputs.run_id }}
+        env:
+          GH_REPO: ${{ github.repository }}
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh run watch ${{ inputs.run_id }} > /dev/null 2>&1
+          gh run rerun ${{ inputs.run_id }} --failed