feat(admin): deep-linkable console URLs, stop collapsing unknown paths to /admin

The root catch-all page ([...slug].vue) redirected every unknown URL to
/admin, and the worker fell back to the SPA for any path — so no matter
what page was opened, the URL ended up at baseurl/admin.

- Extract the console into ConsolePage.vue; the active tab now mirrors
  the URL path: /admin (groups), /admin/groups, /admin/logs, /admin/audit
  (tab switches use router.replace; unknown slugs render 404)
- admin.vue and admin/[slug].vue become thin wrappers
- Delete the root [...slug].vue catch-all redirect
- server.ts: notFound serves ASSETS (SPA + _nuxt chunks) only for
  /admin-prefixed paths; every other unknown URL returns a JSON 404

docs/zh/guide/configuration.md

@@ -56,6 +56,8 @@ WebHooker 内置了位于 `/admin` 的配置控制台，可在浏览器中管理
 
 ### 端点
 
+控制台以 SPA 形式挂在 `/admin`，各标签页可通过 URL 路径直达（`/admin/groups`、`/admin/logs`、`/admin/audit`）。`/admin` 之外且未匹配下方端点的 URL 直接返回 `404`，不会再被吞进控制台。
+
 | 端点                                  | 说明                                 |
 | ------------------------------------- | ------------------------------------ |
 | `GET /admin`                          | 配置控制台页面                       |