fix(scanner) artist stats not refreshing during quick scan and after missing file deletion (#4269)

* Fix artist not being marked as touched during quick scans

When a new album is added during quick scans, artists were not being
marked as 'touched' due to media files having older modification times
than the scan completion time.

Changes:
- Add 'updated_at' to artist Put() columns in scanner to ensure
  timestamp is set when artists are processed
- Simplify RefreshStats query to check artist.updated_at directly
  instead of complex media file joins
- Artists from new albums now properly get refreshed in later phases

This fixes the issue where newly added albums would have incomplete
artist information after quick scans.

* fix(missing): refresh artist stats in background after deleting missing files

Signed-off-by: Deluan <deluan@navidrome.org>

* fix(request): add InternalAuth to user context

Signed-off-by: Deluan <deluan@navidrome.org>

* Add comprehensive test for artist stats update during quick scans

- Add test that verifies artist statistics are correctly updated when new files are added during incremental scans
- Test ensures both overall stats (AlbumCount, SongCount) and role-specific stats are properly refreshed
- Validates fix for artist stats not being refreshed during quick scans when new albums are added
- Uses real artist repository instead of mock to verify actual stats calculation behavior

---------

Signed-off-by: Deluan <deluan@navidrome.org>

server/nativeapi/missing.go

@@ -10,6 +10,7 @@ import (
 	"github.com/deluan/rest"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/model"
+	"github.com/navidrome/navidrome/model/request"
 	"github.com/navidrome/navidrome/utils/req"
 )
 
@@ -89,6 +90,17 @@ func deleteMissingFiles(ds model.DataStore, w http.ResponseWriter, r *http.Reque
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
+
+	// Refresh artist stats in background after deleting missing files
+	go func() {
+		bgCtx := request.AddValues(context.Background(), r.Context())
+		if _, err := ds.Artist(bgCtx).RefreshStats(true); err != nil {
+			log.Error(bgCtx, "Error refreshing artist stats after deleting missing files", err)
+		} else {
+			log.Debug(bgCtx, "Successfully refreshed artist stats after deleting missing files")
+		}
+	}()
+
 	writeDeleteManyResponse(w, r, ids)
 }