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).

engine.spec

@@ -5,9 +5,8 @@
 import os
 from PyInstaller.utils.hooks import collect_dynamic_libs, collect_data_files
 
-# Native DLL cho pedalboard va soundfile (Windows .pyd/.dll, Linux .so)
-binaries = collect_dynamic_libs('pedalboard')
-binaries += collect_dynamic_libs('soundfile')
+# Native DLL cho soundfile (Windows .pyd/.dll, Linux .so)
+binaries = collect_dynamic_libs('soundfile')
 
 # Root tuyet doi cua thu muc chua spec — dung cho cac datas KHONG nam trong
 # package 'app' (vd thu muc md/). Cac assets cua app (static/templates/models)
@@ -89,12 +88,7 @@ _hidden = [
     'uvicorn.protocols.http.auto',
     'uvicorn.protocols.websockets',
     'uvicorn.protocols.websockets.auto',
-    'pedalboard',
-    # C++ ExternalPlugin.h import pedalboard.midi_utils khi tao VST3Plugin
-    # (py::module_::import) - PyInstaller khong thay duoc import tu C++, phai
-    # khai bao hiddenimport thu cong (thieu -> "No module named
-    # 'pedalboard.midi_utils'" khi /midi-render).
-    'pedalboard.midi_utils',
+    # pedalboard (GPL-3.0) DA XOA — native_bridge thay the (xem PLAN_REPLACE_PEDALBOARD_NATIVE_BRIDGE.md)
     'soundfile',
     'sf2utils',
     # pyfluidsynth (fluidsynth.py cffi) - render soundfont native cho