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