fix(midi): route MIDI live via masterBus, fix media explorer drag, add action logging

- TrackInstrument: gate native live path (SF/VSTi WASAPI bridge bypassed
  masterBus -> mastering FX + main out VU dead). Fallback to SonicSF WASM
  through masterBus.input; native kept for offline render only.
- MEDIA_LIBRARY_SAMPLES: rename MIDI_Loop_02_Bass/03_Lead/05_Bass to match
  actual /static/midi files (drag was 404 -> parse error).
- Add SonicAppLogger (console + POST /api/v1/logs) wired to: instrument load
  error, VSTi autosample fail, MIDI item -> mastering fx chain, play -> main
  out, drag MIDI errors (media explorer + window explorer).
- Add backend /api/v1/logs endpoint (server-side log, no DB).

app/static/js/services/trackInstrument.js

@@ -22,7 +22,15 @@ window.TrackInstrument = window.TrackInstrument || {};
 
     // Loại engine native cho track: 'sf' (soundfont), 'vst3'/'vst2' (VSTi có
     // plugin_id) hay null (không native được → fallback WASM/autosample).
+    // T15-regression fix: native live (SF/VSTi qua WASAPI bridge) phát thẳng ra
+    // OS device — BỎ QUA WebAudio masterBus → mastering FX + Main out VU không
+    // nhận tín hiệu. Gate native live path: luôn fallback WASM (SonicSF/
+    // autosample) qua masterBus.input. Native vẫn dùng cho OFFLINE render
+    // (scheduleNativeSfItem / /api/v1/native/render) — không đi qua hàm này.
+    // ponytail: re-enable live native khi C++ bridge có capture/readback →
+    // set window.__SONICFORGE_NATIVE_LIVE = true.
     TrackInstrument.prototype._nativeKind = function () {
+        if (!window.__SONICFORGE_NATIVE_LIVE) return null;
         try {
             if (this.sfId) return 'sf';
             if (window.SonicNativeAudio && this.synthEngine && this.synthEngine.plugin_id) {