Rework repo buttons (#20602, #20718) (#20719)

Rework repo buttons (#20602, #20718) (#20719)

* Rework repo buttons (#20602)

* Rework repo buttons

- Replace "New PR" and "Go to File" button with Icon Button
- Move all "Add File" actions into a dropdown button
- Remove most custom styling of clone buttons
- Margin and wiki tweaks

Buttons are now all equal height, mobile layout wraps gracefully.

Fixes: https://github.com/go-gitea/gitea/issues/13671
Replaces: https://github.com/go-gitea/gitea/pull/20375

* Restore history button and hide add button when unable to add (#20718)

Fix two regressions from #20602:

- Restore the 'History' button that was previously unable to render
  because it's show condition was never hit
- Hide the 'Add File' button when there would be no items in the
  dropdown.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>