feat: 左侧导航改版与 Python 镜像管理

- 应用外壳换成 stash-ui Layout：左侧导航（任务调度 / Python 镜像）+ 页面标题区，窄屏折叠为顶部导航
- 新增 python_mirrors 表与 CRUD/设默认接口，内置清华、阿里云、中科大、PyPI 官方
- Python 脚本任务运行时注入默认镜像的 PIP_INDEX_URL / UV_INDEX_URL，任务自身环境变量优先
- 新增镜像管理页与表单，支持新增、编辑、启用/停用、设默认、删除
- 重新生成 OpenAPI 与 TS 类型；补齐后端镜像测试、前端单测与 e2e，修复窄屏页面被宽表格撑开

frontend/e2e/dashboard.spec.ts

@@ -246,7 +246,9 @@ test('renders without external network access', async ({ page }) => {
   })
 
   await page.goto('/')
-  await expect(page.getByRole('heading', { name: 'TaskPilot' })).toBeVisible()
+  await expect(
+    page.getByRole('heading', { name: '任务调度' }),
+  ).toBeVisible()
 
   const state = await page.evaluate(async () => {
     // 字体二进制不入库；未生成时应回退系统字体，而不是报错。
@@ -331,3 +333,47 @@ test('keeps a long run log scrollable without rendering every line', async ({
     fullPage: true,
   })
 })
+
+test('manages python package mirrors', async ({ page, request }) => {
+  const headers = await authHeaders(request)
+
+  // 失败重跑时先清理上一次留下的测试镜像，并把默认源还原。
+  const existing = await request.get('/api/v1/python/mirrors')
+  expect(existing.ok()).toBeTruthy()
+  const existingMirrors = (await existing.json()) as Array<{
+    id: string
+    index_url: string
+  }>
+  for (const mirror of existingMirrors) {
+    if (mirror.index_url.includes('pypi.e2e.example')) {
+      await request.delete(`/api/v1/python/mirrors/${mirror.id}`, { headers })
+    }
+  }
+  await request.post('/api/v1/python/mirrors/tsinghua/default', { headers })
+
+  await page.goto('/mirrors')
+  await expect(
+    page.getByRole('heading', { name: 'Python 镜像' }),
+  ).toBeVisible()
+  await expect(page.getByRole('row', { name: /清华 TUNA/ })).toBeVisible()
+
+  await page.getByRole('button', { name: '+ 新增镜像' }).click()
+  const dialog = page.getByRole('dialog', { name: '新增 Python 镜像' })
+  await dialog.getByLabel('名称').fill('E2E 镜像')
+  await dialog.getByLabel('索引地址').fill('https://pypi.e2e.example/simple')
+  await dialog.getByRole('button', { name: '保存' }).click()
+
+  const row = page.getByRole('row', { name: /E2E 镜像/ })
+  await expect(row).toBeVisible()
+  await row.getByRole('button', { name: '设为默认' }).click()
+  await expect(row.getByText('默认', { exact: true })).toBeVisible()
+
+  await row.getByRole('button', { name: '删除' }).click()
+  await page
+    .getByRole('dialog', { name: /删除镜像/ })
+    .getByRole('button', { name: '确认删除' })
+    .click()
+  await expect(row).toHaveCount(0)
+
+  await request.post('/api/v1/python/mirrors/tsinghua/default', { headers })
+})