Add always-on RLog at the four ImageRegistry lifecycle points (restore,
remove/ReleaseImage, collectGarbage, clearProvisionalFlag) so a brown
placeholder (registry lookup returns nil) can be diagnosed from a debug
log captured at normal speed. DLog perturbs the async restore/GC timing
enough to hide the race, so RLog is required here.

Each line is tagged "ImageRegistry:" and carries the image code. The two
smoking guns: "GC reap still-provisional code N" (mark never cleared the
provisional flag during interval-tree fixup) and "clear provisional for
code N (MISSING: no registry entry)" (a mark tried to un-provision a code
already removed by dealloc).