phase4: Linux native_bridge build (Docker) — sfizz from source, --render SF2/SFZ

- Dockerfile: build sfizz tu native_bridge/sfizz-src (hoac git clone v1.2.3),
  sed fix sfizz.pc (-llibsfizz -> -lsfizz), cmake bridge voi 3 flag SMTG OFF
  (VSTGUI/plugin/hosting examples) — bridge headless chi can --render.
- CMakeLists: nhanh non-WIN32 build daw_vst_bridge tu main_linux.cpp +
  RenderJob.cpp + NativeInstrumentEngine.cpp (SF2/SF3 + SFZ; VST3/VST2
  hosting Windows-only, guard #ifdef _WIN32). gui_probe/plugin_host/
  seh_channel_test chi build tren Windows.
- RenderJob.cpp: JSON parser (sheredom json.h) khong con phu thuoc
  HAVE_VST3SDK — render SF2/SFZ chay duoc khong can VST3 SDK.
- NativeInstrumentEngine.cpp: guard windows.h/VST3/VST2/Sandbox/SEH.
- main.cpp: g_engine unconditional + guard disable_ime_contexts (_WIN32).
- engine.spec: bo pedalboard collect_dynamic_libs + hidden imports.
- vst_engine/render_engine: DecentSampler -> NotImplementedError + huong
  dan convert .dspreset -> .vstpreset; pianobook fallback synth.
- Verified: WSL Ubuntu 24.04 build OK, bridge Linux --render SF2 ra WAV
  44100 stereo peak 1575; Python tests 115 passed 1 skipped.
- Dockerfile build chua test duoc (may khong co Docker).

app/core/render_engine.py

@@ -7,7 +7,6 @@ from app.config import settings
 from app.core.vst_engine import (
     render_midi_events_to_audio,
     PluginManager,
-    DecentSamplerManager,
     HAS_PEDALBOARD,
     HAS_PYFLUIDSYNTH,
     apply_preset_to_plugin,
@@ -204,35 +203,16 @@ class PythonRenderEngine:
                             vst = plugin_mgr.load_vst(instrument_id) if instrument_id else None
 
                             if instrument_source == "pianobook":
+                                # Phase 4 (§3.4): .dspreset không hỗ trợ nữa (pedalboard
+                                # GPL-3.0 gỡ; spike load .dspreset fail). Chặn + fallback synth.
                                 dspreset_path = track.get("dspreset_path", "")
-                                if dspreset_path and os.path.exists(dspreset_path) and HAS_PEDALBOARD:
-                                    from pedalboard import Pedalboard
-                                    ds_manager = DecentSamplerManager()
-                                    try:
-                                        vst = ds_manager.create_decent_sampler_instance(dspreset_path)
-                                        midi_messages = PluginManager.midi_events_to_messages(
-                                            midi_events, bpm, self.sample_rate
-                                        )
-                                        total_needed = 0
-                                        for ev in midi_events:
-                                            end_sec = (ev.get("start_beat", 0) + ev.get("duration_beats", 1)) * (60.0 / bpm)
-                                            dur_samples = int(end_sec * self.sample_rate)
-                                            if dur_samples > total_needed:
-                                                total_needed = dur_samples
-                                        total_needed = max(total_needed, 1024)
-                                        silent = np.zeros((2, total_needed), dtype=np.float32)
-                                        # pedalboard >= 0.9: instrument KHÔNG vào Pedalboard container
-                                        synth_buffer = vst(midi_messages, sample_rate=self.sample_rate,
-                                                           duration=total_needed / float(self.sample_rate), num_channels=2)
-                                    except Exception as e:
-                                        logger.warning(f"[RenderEngine] DecentSampler/Pianobook error: {e}")
-                                        synth_buffer = render_midi_events_to_audio(
-                                            midi_events=midi_events, sr=self.sample_rate, bpm=bpm, instrument='synth'
-                                        )
-                                else:
-                                    synth_buffer = render_midi_events_to_audio(
-                                        midi_events=midi_events, sr=self.sample_rate, bpm=bpm, instrument='synth'
-                                    )
+                                logger.warning(
+                                    "[RenderEngine] Pianobook track bỏ qua: .dspreset không còn hỗ trợ. "
+                                    "Convert sang .vstpreset (DecentSampler → Save preset) rồi gán lại track."
+                                )
+                                synth_buffer = render_midi_events_to_audio(
+                                    midi_events=midi_events, sr=self.sample_rate, bpm=bpm, instrument='synth'
+                                )
                             elif instrument_id and not instrument_id.startswith("sf_"):
                                 # VSTi track: native_bridge --render (SF_RENDER_ENGINE=bridge)
                                 # thay pedalboard; ngược lại giữ pedalboard path cũ.