fix(backend): match files when Navidrome stem desyncs by release suffix

After the embedded-title change (recognize vs "recognize - Single"),
Navidrome's title-derived stem can drop the "- Single"/"- EP" suffix the
on-disk filename still carries, so _findFileByStem matched neither exact nor
suffix and every fallback failed -> "File not found on disk" on edit/delete.
Now also match on the structured prefix in both directions.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/novasonic-server.js

@@ -119,7 +119,12 @@ function _findFileByStem(dir, titleStem, depth = 0) {
         // Match: exact, or "Artist - Title" ending with our title stem
         if (bareStem === normTitle ||
             bareStem.endsWith(' - ' + normTitle) ||
-            bareStem.endsWith(normTitle)) {
+            bareStem.endsWith(normTitle) ||
+            // Release-suffix desync: Navidrome's title-derived stem ("… - recognize")
+            // may lack the "- Single"/"- EP" suffix the on-disk filename still carries
+            // ("… - recognize - single"), or vice-versa. Match on the structured prefix.
+            bareStem.startsWith(normTitle + ' - ') ||
+            normTitle.startsWith(bareStem + ' - ')) {
           return path.join(dir, entry.name);
         }
       }