The auto-save mount effect only cleared `mountedRef` in its cleanup and never
re-set it to true on setup. Under React StrictMode the initial
setup/cleanup/setup cycle therefore leaves `mountedRef.current` pinned to false
for the component's whole life. A successful save then never reaches the
terminal branch (`succeeded && mountedRef.current`), so the status is stranded
on "saving" and the success toast never fires — the settings save indicator
spins forever even though the PATCH returned 200.
Set `mountedRef.current = true` on every mount so the flag reflects the live
component. Shared by all auto-saved settings (repositories, GitHub, etc.).
Add a StrictMode regression test asserting onSuccess still fires.
