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/src/api/client.ts

@@ -26,6 +26,11 @@ export type DirectoryListingResponse =
   components['schemas']['DirectoryListingResponse']
 export type TaskStats = components['schemas']['TaskStatsResponse']
 export type ScheduledTask = components['schemas']['ScheduledTaskResponse']
+export type PythonMirror = components['schemas']['PythonMirrorResponse']
+export type CreatePythonMirrorRequest =
+  components['schemas']['CreatePythonMirrorRequest']
+export type UpdatePythonMirrorRequest =
+  components['schemas']['UpdatePythonMirrorRequest']
 
 export interface TaskFilters {
   q?: string
@@ -303,3 +308,42 @@ export function fetchStats(signal?: AbortSignal): Promise<TaskStats> {
 export function fetchSchedule(signal?: AbortSignal): Promise<ScheduledTask[]> {
   return requestJson<ScheduledTask[]>('/api/v1/schedule', { signal })
 }
+
+/** Python 包镜像（默认镜像会在脚本任务运行时注入 pip / uv 环境变量）。 */
+export function listPythonMirrors(
+  signal?: AbortSignal,
+): Promise<PythonMirror[]> {
+  return requestJson<PythonMirror[]>('/api/v1/python/mirrors', { signal })
+}
+
+export function createPythonMirror(
+  request: CreatePythonMirrorRequest,
+): Promise<PythonMirror> {
+  return requestJson<PythonMirror>('/api/v1/python/mirrors', {
+    method: 'POST',
+    body: JSON.stringify(request),
+  })
+}
+
+export function updatePythonMirror(
+  id: string,
+  request: UpdatePythonMirrorRequest,
+): Promise<PythonMirror> {
+  return requestJson<PythonMirror>(`/api/v1/python/mirrors/${id}`, {
+    method: 'PUT',
+    body: JSON.stringify(request),
+  })
+}
+
+export function deletePythonMirror(id: string): Promise<void> {
+  return requestJson<void>(`/api/v1/python/mirrors/${id}`, {
+    method: 'DELETE',
+  })
+}
+
+export function setDefaultPythonMirror(id: string): Promise<PythonMirror> {
+  return requestJson<PythonMirror>(
+    `/api/v1/python/mirrors/${id}/default`,
+    { method: 'POST' },
+  )
+}