Use a dark scrim for MobileOverlayPanel instead of a translucent background so
it dims the rest of the screen like the sessions sheet.
Rework MobileSurfaceShell to mirror that structure: the scrim is the fixed
parent's background with a quick fade (keeping it on a compositing layer iOS
Safari clips to the viewport), and the sheet is a flex child sized to leave the
top safe area dimmed — dropping the old top shadow that pooled at the corners.
Mount Files/Changes/Settings only while open so each recomputes its
safe-area layout fresh, fixing intermittent top-inset dimming, and drop the
dim behind the header overflow menu to avoid a scrim-to-scrim flicker on
select.
Bohdan Triapitsyn
f11d56d80c