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).

Dockerfile

@@ -37,6 +37,33 @@ RUN pip install --no-cache-dir -r requirements.txt
 
 COPY . .
 
+# ── Build native_bridge (Linux) — thay pedalboard GPL-3.0 ──────────────────
+# Xem PLAN_REPLACE_PEDALBOARD_NATIVE_BRIDGE.md §4. sfizz khong co trong apt
+# Debian → build tu nguon vendored (native_bridge/sfizz-src, co trong build
+# context) hoac git clone fallback khi thieu. Bridge chay --render duoi
+# Xvfb :99 (DISPLAY da set o tren) — khong can GUI plugin editor.
+RUN apt-get update && apt-get install -y --no-install-recommends \
+        cmake pkg-config libfluidsynth-dev libfreetype-dev git \
+    && rm -rf /var/lib/apt/lists/* \
+    && if [ -d native_bridge/sfizz-src ]; then cp -r native_bridge/sfizz-src /tmp/sfizz; \
+       else git clone --recursive --depth 1 --branch v1.2.3 https://github.com/sfztools/sfizz.git /tmp/sfizz; fi \
+    && cmake -S /tmp/sfizz -B /tmp/sfizz/build -DCMAKE_BUILD_TYPE=Release \
+           -DSFIZZ_SHARED=ON -DSFIZZ_JACK=OFF -DSFIZZ_RENDER=OFF -DSFIZZ_TESTS=OFF \
+           -DSFIZZ_BENCHMARKS=OFF -DSFIZZ_DEMOS=OFF -DSFIZZ_DEVTOOLS=OFF \
+           -DSFIZZ_GIT_SUBMODULE_CHECK=OFF -DBUILD_TESTING=OFF \
+    && cmake --build /tmp/sfizz/build --target sfizz_shared -j"$(nproc)" \
+    && cmake --install /tmp/sfizz/build \
+    && sed -i 's/-llibsfizz/-lsfizz/' /usr/local/lib/pkgconfig/sfizz.pc \
+    && cmake -S native_bridge -B /tmp/bridge-build -DCMAKE_BUILD_TYPE=Release \
+           -DSMTG_ENABLE_VST3_PLUGIN_EXAMPLES=OFF \
+           -DSMTG_ENABLE_VST3_HOSTING_EXAMPLES=OFF \
+           -DSMTG_ENABLE_VSTGUI_SUPPORT=OFF \
+    && cmake --build /tmp/bridge-build --target daw_vst_bridge -j"$(nproc)" \
+    && mkdir -p /app/install \
+    && cp /tmp/bridge-build/daw_vst_bridge /app/install/ \
+    && rm -rf /tmp/sfizz /tmp/sfizz/build /tmp/bridge-build
+
+
 # Copy VST3 plugins if present
 COPY ./vst_plugins/ /opt/daw_engine/vst3/