Replace single-page layout with a frameset: left navigation frame
with repo dropdown and page links, right content frame showing
the selected page. Split the repo page into separate sub-pages:
branches, changes, remote, and manage.
Uses <frameset> for maximum compatibility with ancient browsers
(Netscape 2+, IE 3+). Clone and delete forms target _top to
reload the full frameset when the repo list changes.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
