fix(264): record library-level LastScan after a successful local scan

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

ErsatzTV.Scanner/Application/MediaSources/Commands/ScanLocalLibraryHandler.cs

@@ -1,4 +1,4 @@
-using System.Diagnostics;
+using System.Diagnostics;
 using ErsatzTV.Core;
 using ErsatzTV.Core.Domain;
 using ErsatzTV.Core.Interfaces.Repositories;
@@ -65,6 +65,7 @@ public class ScanLocalLibraryHandler : IRequestHandler<ScanLocalLibrary, Either<
         _scannerProxy.SetBaseUrl(baseUrl);
 
         var scanned = false;
+        var anyFailed = false;
 
         for (var i = 0; i < localLibrary.Paths.Count; i++)
         {
@@ -145,6 +146,10 @@ public class ScanLocalLibraryHandler : IRequestHandler<ScanLocalLibrary, Either<
                     libraryPath.LastScan = DateTime.UtcNow;
                     await _libraryRepository.UpdateLastScan(libraryPath);
                 }
+                else
+                {
+                    anyFailed = true;
+                }
             }
 
             await _scannerProxy.UpdateProgress(progressMax, cancellationToken);
@@ -152,6 +157,15 @@ public class ScanLocalLibraryHandler : IRequestHandler<ScanLocalLibrary, Either<
 
         sw.Stop();
 
+        // the library-level LastScan drives the "last scanned" / "Never scanned" badge in the API and SPA,
+        // and is separate from the per-path LastScan that gates the refresh interval above. Only record it
+        // when every path that ran succeeded, mirroring the remote scanners (which set it solely on IsRight).
+        if (scanned && !anyFailed)
+        {
+            localLibrary.LastScan = DateTime.UtcNow;
+            await _libraryRepository.UpdateLastScan(localLibrary);
+        }
+
         if (scanned)
         {
             _logger.LogDebug(