fix(410): log scan cancellation below ERROR (user-initiated, not a failure)

Scan cancellation surfaces as ScanCanceled, an ordinary BaseError, so all
four scan handlers (Jellyfin/Emby/Plex/local) logged it at ERROR alongside
genuine failures. A user cancelling a scan (or a container restart mid-scan)
is not an error; this was training operators to ignore scanner ERROR lines,
corrosive precisely because #264 showed scanner failures can be silent.

Each handler's Left-result loop now branches on `error is ScanCanceled`:
logs Information ("Scan of {Name} was canceled") for cancellation, keeps
LogError for every other BaseError. No behavior change to LastScan
stamping (still correctly skipped on any Left, cancellation included).

fixes #410

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -1,6 +1,7 @@
 using System.Diagnostics;
 using ErsatzTV.Core;
 using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Errors;
 using ErsatzTV.Core.Interfaces.Repositories;
 using ErsatzTV.Scanner.Core.Interfaces;
 using ErsatzTV.Scanner.Core.Interfaces.Metadata;
@@ -152,13 +153,23 @@ public class ScanLocalLibraryHandler : IRequestHandler<ScanLocalLibrary, Either<
 
                     // a failed path now suppresses the library-level scan time below, so without this the
                     // user sees "Never scanned" with nothing explaining why. The remote scanners log the
-                    // same way.
+                    // same way. A cancellation is user-initiated, not a failure, so it's logged separately
+                    // at a lower level; genuine errors still log at ERROR.
                     foreach (BaseError error in result.LeftToSeq())
                     {
-                        _logger.LogError(
-                            "Error scanning local library path {Path}: {Error}",
-                            libraryPath.Path,
-                            error);
+                        if (error is ScanCanceled)
+                        {
+                            _logger.LogInformation(
+                                "Scan of local library path {Path} was canceled",
+                                libraryPath.Path);
+                        }
+                        else
+                        {
+                            _logger.LogError(
+                                "Error scanning local library path {Path}: {Error}",
+                                libraryPath.Path,
+                                error);
+                        }
                     }
                 }
             }