New UserMenu component owns its own trigger + dropdown + dismissal so the
topbar stays simple. Menu contents: identity row (name + email), theme
toggle (reuses useTweaks so the floating panel and menu stay in sync),
link to /settings, Sign out (calls useOidcAuth().logout).
Dismissal: outside click via a transparent Teleport scrim, Escape, and
route change (watch on route.path → close).
Drops the now-unused useOidcAuth import from OpTopbar.
Ronni Baslund