The docs claimed only a sidecar written here before auto-write was
turned off could be mistaken for an update; in fact the library only
knows when a photo came in or was last developed, so any later rating,
label or metadata change made here can be. Says so, with the headless
fixed clock, the sidecar naming fallback and the walk's limits; the
parity row and what's new also cover relinking moved files, Local
files, offline folders and the `disk` guard. Adds the test that a
sidecar the library auto-wrote is never an update.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
