Initial release — InstaShadow mastering compressor v1.0

Dual-stage compressor (optical + VCA) with output transformer saturation.
- Port-Hamiltonian T4B opto-cell model with implicit trapezoidal integration
- Feed-forward VCA with 7 ratios, 6 attack/release presets, Dual release mode
- 3 transformer types (Nickel/Iron/Steel) with 4x oversampled waveshaping
- Analog-style needle VU meters, horizontal GR meters
- Sidechain HPF, stereo link, independent section bypass
- Full state save/restore, CI/CD for Windows/macOS/Linux

README.md

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+# InstaShadow
+
+Dual-stage mastering compressor plugin (VST3/AU/LV2) inspired by the Shadow Hills Mastering Compressor, built with JUCE.
+
+## Features
+
+- **Optical Compressor** — Port-Hamiltonian T4B opto-cell model with physically accurate two-stage release and CdS memory effect
+- **Discrete VCA Compressor** — Feed-forward Class-A topology with 7 ratio settings (1.2:1 to Flood), 6 attack/release presets, and Dual release mode
+- **Output Transformer** — 3 switchable transformer types (Nickel/Iron/Steel) with frequency-dependent saturation and 4x oversampling
+- **Sidechain HPF** — Variable 20-500 Hz high-pass filter to prevent bass-induced pumping
+- **Stereo Link** — Linked or dual-mono operation
+- **Independent bypass** — Each section can be bypassed separately
+- **GR Metering** — Dedicated optical and discrete gain reduction meters
+- **State save/restore** — All parameters persist with DAW session
+
+## Signal Flow
+
+```
+Input → SC HPF → Optical Comp (T4B) → VCA Comp → Transformer → Output
+```
+
+## Build
+
+Requires [JUCE](https://github.com/juce-framework/JUCE) cloned at `../JUCE` relative to this project.
+
+```bash
+cmake -B build -G "Visual Studio 17 2022" -A x64
+cmake --build build --config Release
+```
+
+## License
+
+GPL-3.0