phase5: mặc định RENDER_ENGINE=bridge, gỡ pedalboard khỏi requirements/source/LICENSE

- config.py: SF_RENDER_ENGINE default 'bridge' (pedalboard GPL-3.0 đã gỡ)
- requirements.txt: bỏ pedalboard==0.9.19
- vst_engine.py: bỏ HAS_PEDALBOARD/check_pedalboard_safe/load_vst/import pedalboard;
  midi_events_to_messages giữ làm utility thuần (không gate pedalboard)
- render_engine.py: bỏ nhánh elif vst and HAS_PEDALBOARD + import thừa
- plugins.py: preview/midi-render chỉ qua native_bridge; guard SF_RENDER_ENGINE=bridge
- runtime.py: _vst_render_available() check bridge exe (SF_BRIDGE_PATH/install/) thay find_spec('pedalboard')
- LICENSE.md/THIRD_PARTY_LICENSES.md: bỏ cảnh báo GPL-3.0 pedalboard, đánh số lại
- tests: bỏ test golden so pedalboard + test requires_pedalboard; 114 passed 0 skip

app/config.py

@@ -67,10 +67,9 @@ class Settings:
     # storage (Windows desktop).
     PRESET_DIR: str = os.path.join(STORAGE_DIR, "presets")
 
-    # Render engine offline (preview/export VSTi): 'pedalboard' (cũ, GPL-3.0)
-    # hoặc 'bridge' (native_bridge --render, MIT). Mặc định pedalboard trong
-    # giai đoạn chuyển; đảo sang 'bridge' ở phase 5
-    # (PLAN_REPLACE_PEDALBOARD_NATIVE_BRIDGE.md).
-    RENDER_ENGINE: str = os.getenv("SF_RENDER_ENGINE", "pedalboard")
+    # Render engine offline (preview/export VSTi): 'bridge' (native_bridge
+    # --render, MIT). Giá trị khác → fallback synth (pedalboard GPL-3.0 đã gỡ
+    # phase 5 — PLAN_REPLACE_PEDALBOARD_NATIVE_BRIDGE.md).
+    RENDER_ENGINE: str = os.getenv("SF_RENDER_ENGINE", "bridge")
 
 settings = Settings()