fix: add missing checks to several API and web handlers (#39501) (#39507)

Backport #39501 by @silverwind

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

routers/web/user/profile.go

@@ -322,6 +322,13 @@ func prepareUserProfileTabData(ctx *context.Context, profileDbRepo *repo_model.R
 
 // ActionUserFollow is for follow/unfollow user request
 func ActionUserFollow(ctx *context.Context) {
+	isOrg := ctx.ContextUser.IsOrganization()
+	if isOrg && !organization.HasOrgOrUserVisible(ctx, ctx.ContextUser, ctx.Doer) ||
+		!isOrg && !user_model.IsUserVisibleToViewer(ctx, ctx.ContextUser, ctx.Doer) {
+		ctx.NotFound(nil)
+		return
+	}
+
 	var err error
 	switch ctx.FormString("action") {
 	case "follow":