Local libraries permanently showed "Never scanned" in the SPA libraries
hub regardless of successful scans, even as item counts updated.
Root cause: ScanLocalLibraryHandler wrote only the path-level
LibraryPath.LastScan (which gates the per-path refresh interval) and
never the library-level Library.LastScan. The read API
(GetAllMediaSourcesForApiHandler) populates the hub's scan-time badge
from Library.LastScan, so that value stayed null forever. The three
remote scanners (Jellyfin/Emby/Plex) already set the library-level
value; only the local scanner did not. Both sides predate #202 — the
SPA hub merely made the missing value visible.
Mirror the remote scanners' semantics: record the library-level scan
time only when the scan actually ran and every path that ran succeeded,
so a skipped (unforced, interval not elapsed) or partially-failed scan
does not claim a successful scan time.
Also de-BOM the touched handler per the fix-as-you-touch charset gate
(#311).
fixes#264
