v1.1 — Improved metering, transformer, and optical cell tuning

- Needle VU meters with spring-mass-damper physics (analog inertia)
- Swappable meter modes: GR needles + input bars, or input needles + GR bars
- GR bar meters fill right-to-left (0dB=empty, -30dB=full)
- Input bar meters fill left-to-right with green color
- Optical cell: normalized parameters (eta=50) for proper audio-level response
- Transformer: removed 3-band crossover artifacts, simplified waveshaping with dry/wet mix
- Nickel/Iron/Steel with distinct but subtle harmonic character
- Layout: optical left, discrete right, meters center, transformer+output bottom center

Source/CompressorEngine.h

@@ -37,6 +37,8 @@ public:
     // --- Metering (audio → GUI) ---
     std::atomic<float> optoGrDb         { 0.0f };
     std::atomic<float> vcaGrDb          { 0.0f };
+    std::atomic<float> inputLevelL      { 0.0f };
+    std::atomic<float> inputLevelR      { 0.0f };
     std::atomic<float> outputLevelL     { 0.0f };
     std::atomic<float> outputLevelR     { 0.0f };