Reusing `/api/v1` from Gitea UI Pages have pros and cons.
Pros:
1) Less code copy
Cons:
1) API/v1 have to support shared session with page requests.
2) You need to consider for each other when you want to change something about api/v1 or page.
This PR moves all dependencies to API/v1 from UI Pages.
Partially replace #16052
