Scanner: new instance with existing sf_scan_state.json
did not populate in-memory _catalog. Now re-inspects
unchanged files to fill catalog on first scan.
Frontend: left column reads instrumentSelectorData.
soundfonts instead of sfPresets (null when no presets).
Click SF in left column triggers on-demand fetch.
Background daemon (30s interval) tracks scanned files via
sf_scan_state.json (size+mtime). Only inspects new/changed SFs.
Catalog served from scanner cache, no full re-scan per request.
Upload/delete trigger immediate re-scan.
3dtours