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/vst_engine.py

@@ -521,25 +521,15 @@ class DecentSamplerManager:
         self.vst_path = vst_path
 
     def create_decent_sampler_instance(self, dspreset_path: str):
-        if not HAS_PEDALBOARD:
-            raise RuntimeError("pedalboard not available")
-        if not os.path.exists(self.vst_path):
-            raise FileNotFoundError(f"DecentSampler VST3 not found at {self.vst_path}")
-        if not os.path.exists(dspreset_path):
-            raise FileNotFoundError(f"Preset file not found at {dspreset_path}")
-
-        plugin = VST3Plugin(self.vst_path)
-
-        abs_preset = os.path.abspath(dspreset_path)
-        preset_dir = os.path.dirname(abs_preset)
-        cwd_before = os.getcwd()
-        try:
-            os.chdir(preset_dir)
-            plugin.load_preset(abs_preset)
-        finally:
-            os.chdir(cwd_before)
-
-        return plugin
+        # Phase 4 (PLAN_REPLACE_PEDALBOARD_NATIVE_BRIDGE.md §3.4): .dspreset là
+        # format riêng của DecentSampler (không phải VST3 state) — spike đã fail
+        # cả trên pedalboard (container: "failed to load data from preset file").
+        # pedalboard GPL-3.0 bị gỡ → chặn Pianobook + hướng dẫn convert.
+        raise NotImplementedError(
+            "Pianobook .dspreset không còn được hỗ trợ (pedalboard GPL-3.0 đã gỡ). "
+            "Chuyển đổi: mở preset trong DecentSampler → save .vstpreset (VST3 state) "
+            "rồi upload .vstpreset qua web UI — native_bridge đọc được."
+        )
 
 
 # ── Preset bridge (Carla ↔ pedalboard) ─────────────────────────────────────