feat(piano-roll): ghost notes + dropdown item switcher + session sync

- MIDI ghost notes: all non-selected items rendered at 25% opacity
- Dropdown at tab title: switch active edit target across all tracks
- Session Sync mode (default): viewport aligned to session bars
- Isolated mode toggle: bar 0, no ghost notes
- Ghost toggle: show/hide ghost layer (only in session mode)
- Auto-scroll to session position in session sync mode
- Bar labels show absolute session bar numbers

app/templates/index.html

@@ -18,6 +18,7 @@
     <script src="/static/js/services/soundfontPlayer.js?v=202607271245"></script>
     <script src="/static/js/services/aiGateway.js?v=202607271016"></script>
     <script src="/static/js/services/dawCommandDispatcher.js?v=202607271016"></script>
+    <script src="/static/js/services/ghostNoteExtractor.js?v=202607271727"></script>
     <script src="/static/js/app.precompiled.js?v=202607271245" defer></script>
     <link rel="stylesheet" href="/static/css/styles.css?v=202607271016">
     <style>