feat: rename song file artist segment when applying romaji override fix

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/novasonic-server.js

@@ -704,6 +704,30 @@ app.post('/api/fix-artist-sort', async (req, res) => {
         });
         fs.renameSync(tmpFile, filePath);
 
+        // Rename the file itself: keep track prefix + title, replace artist segment.
+        // Convention: {NN - }Artist - Title.ext  (separator may be " - " or " – ")
+        const oldBasename = path.basename(filePath);
+        const oldStem     = oldBasename.slice(0, -fileExt.length);
+        // Extract leading track prefix (e.g. "01 - " or "01-15 – ")
+        const trackPrefixMatch = oldStem.match(/^(\d[\d\-]*\s*[-–—]\s*)/);
+        const trackPrefix = trackPrefixMatch ? trackPrefixMatch[1] : '';
+        // Everything after the track prefix: "OldArtist - Title" or just "Title"
+        const afterPrefix = oldStem.slice(trackPrefix.length);
+        // Split on first " - " or " – ": if 2+ segments, first is old artist, rest is title
+        const segments  = afterPrefix.split(/\s+[-–—]\s+/);
+        const titlePart = segments.length >= 2 ? segments.slice(1).join(' - ') : afterPrefix;
+        const safeArtistFile = sanitize(artistSort.split(/[,;&]/)[0].trim());
+        const safeTitlePart  = sanitize(titlePart);
+        const newBasename    = `${trackPrefix}${safeArtistFile} - ${safeTitlePart}${fileExt}`;
+
+        if (newBasename !== oldBasename) {
+          const renamedPath = path.join(path.dirname(filePath), newBasename);
+          if (!fs.existsSync(renamedPath)) {
+            fs.renameSync(filePath, renamedPath);
+            filePath = renamedPath;
+          }
+        }
+
         // Move to correct artist/album folder: {musicPath}/{safeArtistDir}/{albumName}/
         const oldAlbumDir  = path.dirname(filePath);
         const oldArtistDir = path.dirname(oldAlbumDir);