refactor(bridge): split fx bridge, stabilize VST3 host chain, drop old install engines

- remove diagnostic canaries from audio hot path (crackle fix) and
  stuck C5 note raw-MIDI test (Vst2Instrument::init noteOff)
- split native bridge into daw_vst_bridge (VSTi) + fx_vst_bridge (VST FX)
- VST3: processData prepare before setActive, zero input buses, accept
  both .vstpreset and bridge-state blob in RenderJob presets
- native_render/vst_engine: bridge-exe discovery + render_fx_chain + /fx-gui
- delete old install/ engine binaries (install via sidecar+resources now)
- add BUILD_LAYOUT.md, build_selfcheck, tools/ diagnostics

app/api/v1/plugins.py

@@ -701,12 +701,12 @@ async def open_fx_gui(req: FxGuiRequest, current_user: dict = Depends(get_curren
     (exit 0). Không spawn 2 lần cho cùng plugin đang mở (tránh trùng GUI).
     """
     enforce_password_changed(current_user)
-    from app.core.native_render import find_bridge_exe
-    exe = find_bridge_exe()
+    from app.core.native_render import find_fx_bridge_exe
+    exe = find_fx_bridge_exe()
     if not exe:
         raise HTTPException(
             status_code=409,
-            detail="Không tìm thấy bridge native (daw_vst_bridge.exe). "
+            detail="Không tìm thấy bridge native (fx_vst_bridge.exe). "
                    "Hãy chạy bản desktop đã build đầy đủ.",
         )
     plugin_path = (req.path or "").strip()