Fix inconsistent disabled styling on logged-out repo header buttons (#37406)

Make the watch, star, and fork buttons in the repo header consistent for
logged-out users:

- Apply the same look to all three buttons (number labels
included), instead of only the action button being grayed.
- Clicking any of them while logged out now leads to the login page
(with a redirect back) instead of being inert.
- Split the per-button markup out of `header.tmpl` into a dedicated
`templates/repo/header/` folder (`fork.tmpl`, `star.tmpl`,
`watch.tmpl`).

---------

Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/star.go

@@ -11,7 +11,7 @@ import (
 	"code.gitea.io/gitea/services/context"
 )
 
-const tplStarUnstar templates.TplName = "repo/star_unstar"
+const tplStarUnstar templates.TplName = "repo/header/star"
 
 func ActionStar(ctx *context.Context) {
 	err := repo_model.StarRepo(ctx, ctx.Doer, ctx.Repo.Repository, ctx.PathParam("action") == "star")

routers/web/repo/watch.go

@@ -11,7 +11,7 @@ import (
 	"code.gitea.io/gitea/services/context"
 )
 
-const tplWatchUnwatch templates.TplName = "repo/watch_unwatch"
+const tplWatchUnwatch templates.TplName = "repo/header/watch"
 
 func ActionWatch(ctx *context.Context) {
 	err := repo_model.WatchRepo(ctx, ctx.Doer, ctx.Repo.Repository, ctx.PathParam("action") == "watch")