v2.0.9 — the dashboard's Add a submodule section is folded by default

The dashboard's "Add a submodule" card is now collapsed by default, the
same fold the commit log already used. Click its heading to open it; the
choice is kept per user (the preference admin_git_manager_add_submodule)
so it survives a reload. It opens on its own if an add just failed
validation, so the error is never hidden behind the fold, and it still
works as a plain details element with JavaScript off.

Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com