feat(api): list all packages for site administrators (#38968)

Add `GET /admin/packages` so site administrators can review packages
across every owner without querying each owner separately.

It returns the same package version representation as `GET
/packages/{owner}` and supports `page`, `limit`, `type`, and `q`
filters.

---
Assisted by Codet(DeepSeek)

---------

Signed-off-by: bircni <bircni@icloud.com>
Signed-off-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/api/v1/api.go

@@ -1888,6 +1888,7 @@ func Routes() *web.Router {
 				m.Post("/{task}", admin.PostCronTask)
 			})
 			m.Get("/orgs", admin.GetAllOrgs)
+			m.Get("/packages", admin.ListPackages)
 			m.Group("/users", func() {
 				m.Get("", admin.SearchUsers)
 				m.Post("", bind(api.CreateUserOption{}), admin.CreateUser)