Two serving-correctness fixes from review:
- serveMediaFile served a persisted mf embedded image even after EnableMediaFileCoverArt
was turned off (the setting isn't in the config fingerprint, so found rows aren't
reprocessed). Direct mf- URLs now honor the setting at serve time and fall back to
disc/album art.
- The file-backed staleness check compared whole-second mtimes, so a same-second content
replacement (two writes in one second, or timestamp-preserving tools) could serve
different bytes under the old hash + immutable policy. RefMtime is now unix-nanoseconds
(no schema change; int64 column), detecting sub-second changes where the filesystem
records them.
aba7ed925c