Never use /api/v1 from Gitea UI Pages (#19318)

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

web_src/js/features/repo-home.js

@@ -91,7 +91,7 @@ export function initRepoTopicBar() {
       label: 'ui small label'
     },
     apiSettings: {
-      url: `${appSubUrl}/api/v1/topics/search?q={query}`,
+      url: `${appSubUrl}/explore/topics/search?q={query}`,
       throttle: 500,
       cache: false,
       onResponse(res) {