fix(fx-rt): het crackle master FX - limiter attack smooth + crossfade khi bat/tat chain

- NativeInstrumentEngine: kAttack 0.9->0.1 (het zipper khi sum nhieu track)
- app.jsx: crossfade masterFxDryGain/masterFxGain thay hard-rewire graph luc
  activation/deactivation master chain FX; worklet bao 'started' -> ramp dung
  luc; PDC tre sau khi dry silent (tranh gap 80ms)
- sf-fx-realtime.js: fade-in 512 mau luc FILL xong / resume sau underrun
- index.html + addModule: cache-buster v=202608241200
- rebuild app.precompiled.js, copy bundle vao dist/ + src-tauri/resources/
- keo dai fix cac round truoc: FILL 16, FXRT_BURST_MS, REBUFFER, pacing,
  VST GUI click/focus, solo crackle
- them harness + plans/patch scripts

native_bridge/include/NativeInstrumentEngine.h

@@ -165,8 +165,9 @@ public:
 
 private:
     static std::unique_ptr<INativeInstrument> create_instrument(InstrumentType type);
-    // Probe-render 3 notes sau khi load, do peak, tinh makeup de note don ra
-    // ~ -6 dBFS (0.5) - can bang am luong moi engine (VST2/VST3/SF2/SFZ).
+    // Probe-render 3 notes sau khi load, do peak + RMS, tinh makeup de note
+    // don ra ~ -18 dBFS RMS / -6 dBFS peak - can bang am luong moi engine
+    // (VST2/VST3/SF2/SFZ).
     static float calibrate(INativeInstrument* inst, double sampleRate, uint32_t blockSize);
 
     mutable std::mutex mu_;