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/api/v1/plugins.py

@@ -6,8 +6,8 @@ from fastapi.responses import FileResponse
 from pydantic import BaseModel
 from typing import Optional, Any
 from app.config import settings
-from app.core.vst_engine import PluginManager, HAS_PEDALBOARD, HAS_PYFLUIDSYNTH, apply_preset_to_plugin
-from app.core.render_engine import PythonRenderEngine
+from app.core.vst_engine import PluginManager, HAS_PEDALBOARD, HAS_PYFLUIDSYNTH, apply_preset_to_plugin, render_soundfont_midi_to_audio
+from app.core.render_engine import PythonRenderEngine, _find_sf2_path, _find_default_sf2
 from app.core.soundfont_inspector import SoundFontInspector
 from app.core.soundfont_converter import SoundFontConverter
 from app.core.soundfont_scanner import SoundFontAutoScanner
@@ -992,6 +992,73 @@ def _render_midi_notes_pedalboard(instrument_id: str, notes: list, bpm: float,
     return out_path, buf.shape[1] / float(sample_rate)
 
 
+class SoundfontRenderRequest(BaseModel):
+    """Render MIDI notes → WAV bằng soundfont THẬT qua native FluidSynth
+    (pyfluidsynth) — luồng âm instrument cho môi trường STANDALONE (xử lí
+    trực tiếp trên OS; docker dùng FluidSynthWASM ở client)."""
+    soundfont_id: Optional[str] = None
+    soundfont_path: Optional[str] = None
+    bank: int = 0
+    program: int = 0
+    notes: list = []
+    bpm: float = 120.0
+    sample_rate: int = 44100
+
+
+@router.post("/soundfont-render")
+async def soundfont_render(req: SoundfontRenderRequest, current_user: dict = Depends(get_current_user)):
+    """Preview/play MIDI notes bằng âm soundfont thật — native FluidSynth trên OS.
+
+    Khác FluidSynthWASM (docker): âm render server-side bằng pyfluidsynth, trả
+    WAV để client play. Dùng cho: preview/keyboard, play MIDI item khi chạy
+    transport ở môi trường standalone."""
+    enforce_password_changed(current_user)
+    if not req.notes:
+        raise HTTPException(status_code=400, detail="Chưa có nốt nhạc để render")
+    if not HAS_PYFLUIDSYNTH:
+        raise HTTPException(status_code=501, detail="pyfluidsynth không khả dụng — không render được soundfont native")
+    # Resolve path: soundfont_path → soundfont_id (upload/user dirs) → default
+    sf_path = (req.soundfont_path or "").strip()
+    if not sf_path and req.soundfont_id:
+        sf_path = _find_sf2_path(req.soundfont_id)
+    if not sf_path or not os.path.exists(sf_path):
+        sf_path = _find_default_sf2()
+    if not sf_path or not os.path.exists(sf_path):
+        raise HTTPException(status_code=404, detail="SoundFont không tìm thấy — hãy thêm soundfont vào Plugin Manager")
+    midi_events = [{
+        "note": int(n.get("pitch", 60)),
+        "start_beat": float(n.get("start_beat", 0)),
+        "duration_beats": float(n.get("duration_beats", 1)),
+        "velocity": int(float(n.get("velocity", 0.8)) * 127),
+    } for n in req.notes]
+    out_path = os.path.join(settings.PROCESSED_DIR, f"sf_{uuid.uuid4().hex[:10]}.wav")
+    try:
+        audio = render_soundfont_midi_to_audio(
+            midi_events, sf_path,
+            bank=req.bank, program=req.program,
+            sr=req.sample_rate, bpm=req.bpm,
+        )
+        sf.write(out_path, audio.T, req.sample_rate)
+        return {
+            "success": True,
+            "file_id": os.path.basename(out_path),
+            "url": f"/static/audio/processed/{os.path.basename(out_path)}",
+            "path": out_path,
+            "duration_sec": round(audio.shape[1] / float(req.sample_rate), 3),
+            "render_mode": "native-fluidsynth",
+            "soundfont": os.path.basename(sf_path),
+        }
+    except HTTPException:
+        raise
+    except Exception as e:
+        try:
+            if os.path.exists(out_path):
+                os.remove(out_path)
+        except Exception:
+            pass
+        raise HTTPException(status_code=500, detail=f"Render soundfont thất bại: {e}")
+
+
 class CarlaPlayNotesRequest(BaseModel):
     """Phát dãy MIDI notes qua Carla bridge (OSC, realtime) — preview khi
     pedalboard không render được plugin (VD VST2). Cần Carla đang chạy với