feat: tách luồng âm instrument theo môi trường — docker dùng FluidSynthWASM, standalone dùng native pyfluidsynth (+Carla VSTi)

- runtime: detect()/capabilities() trả environment (docker|standalone)
- vst_engine: render_soundfont_midi_to_audio (pyfluidsynth native, event-stream, release tail)
- plugins: POST /soundfont-render — render MIDI notes -> WAV (auth, fallback default SF)
- frontend: SonicRuntime.environment + dataset.environment; app.jsx route preview/transport:
  standalone+SF -> soundfont-render WAV (playNativeSfNote/scheduleNativeSfItem),
  docker giữ WASM, VSTi standalone giữ Carla bridge

app/core/runtime.py

@@ -332,10 +332,12 @@ def detect() -> dict:
     platform = _detect_platform()
     runtime = _detect_runtime()
     carla = find_carla() if runtime == "desktop" else ""
+    docker = _in_docker()
     return {
         "platform": platform,
         "runtime": runtime,                 # "desktop" | "headless"
-        "docker": _in_docker(),
+        "docker": docker,
+        "environment": "docker" if docker else "standalone",  # luồng âm instrument: docker→FluidSynthWASM, standalone→native OS
         "has_display": _has_display(),
         "tauri_bridge": _tauri_bridge_ready(),
         "carla_path": carla,
@@ -375,6 +377,7 @@ def capabilities() -> dict:
         "runtime": d["runtime"],
         "platform": d["platform"],
         "docker": d["docker"],
+        "environment": d["environment"],
         "features": features,
         "default_dirs": {
             "vst": d["default_vst_dirs"],