fix: add missing checks to several API and web handlers (#39501)

Several handlers skipped checks that their sibling routes or settings already enforce. This brings them in line.

- Push mirror API honors `DISABLE_NEW_PUSH` and checks the caller's permission
- Media API serves small files with the usual content headers
- Issue attachment API ignores comment attachments
- Push-to-create respects `FORCE_PRIVATE`
- Profile feeds and follow actions respect `ENABLE_FEED` and owner visibility
- Tag delete route refuses release tags
- Refresh token grant only accepts refresh tokens
- Gitea migrations bound the source's page size

Co-authored-by: bircni <bircni@icloud.com>

tests/integration/api_issue_attachment_test.go

@@ -38,6 +38,11 @@ func TestAPIGetIssueAttachment(t *testing.T) {
 	apiAttachment := DecodeJSON(t, resp, &api.Attachment{})
 
 	unittest.AssertExistsAndLoadBean(t, &repo_model.Attachment{ID: apiAttachment.ID, IssueID: issue.ID})
+
+	commentAttachment := unittest.AssertExistsAndLoadBean(t, &repo_model.Attachment{ID: 3, RepoID: repo.ID})
+	req = NewRequest(t, "GET", fmt.Sprintf("/api/v1/repos/%s/%s/issues/%d/assets/%d", repoOwner.Name, repo.Name, unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: commentAttachment.IssueID}).Index, commentAttachment.ID)).
+		AddTokenAuth(token)
+	session.MakeRequest(t, req, http.StatusNotFound)
 }
 
 func TestAPIListIssueAttachments(t *testing.T) {