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.Tests/Application/MediaSources/ScanLocalLibraryHandlerTests.cs

@@ -1,5 +1,6 @@
 using ErsatzTV.Core;
 using ErsatzTV.Core.Domain;
+using ErsatzTV.Core.Errors;
 using ErsatzTV.Core.Interfaces.Repositories;
 using ErsatzTV.Scanner.Application.MediaSources;
 using ErsatzTV.Scanner.Core.Interfaces;
@@ -96,6 +97,27 @@ public class ScanLocalLibraryHandlerTests
             ShouldHaveLogged("Error scanning local library path /movies: scan failed");
         }
 
+        [Test]
+        public async Task Should_Not_Log_Error_When_A_Path_Scan_Is_Canceled()
+        {
+            ScanResult(Left<BaseError, Unit>(new ScanCanceled()));
+
+            await Handler().Handle(
+                new ScanLocalLibrary("http://ersatztv.example", _library.Id, true),
+                CancellationToken.None);
+
+            // a user-initiated cancellation is not a failure and must not be logged at ERROR (#410);
+            // it's still correctly excluded from the "last scan" stamp, same as any other failure
+            _library.LastScan.ShouldBeNull();
+            await _libraryRepository.DidNotReceive().UpdateLastScan(Arg.Any<Library>());
+
+            _logger.ReceivedCalls()
+                .Any(call => call.GetArguments().ElementAtOrDefault(2)?.ToString()
+                    == "Error scanning local library path /movies: Scan was canceled")
+                .ShouldBeFalse();
+            ShouldHaveLogged("Scan of local library path /movies was canceled");
+        }
+
         [Test]
         public async Task Should_Not_Set_Library_LastScan_When_A_Later_Path_Fails()
         {