Replace track count with source in results table

Changed table columns from Title | Duration | Tracks
to Title | Source | Duration - more useful to see where
the MIDI is from (BitMidi, etc.) than track count.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/main.ts

@@ -190,8 +190,8 @@ class MotifApp {
 
       row.innerHTML = `
         <td>${result.title}</td>
+        <td class="source-col">${result.source}</td>
         <td class="duration-col">${result.parsed ? Math.round(result.parsed.durationSec) + 's' : '?'}</td>
-        <td class="tracks-col">${result.parsed ? result.parsed.tracks.length : '?'}</td>
       `;
 
       // Make entire row clickable