Initial commit: InstaLPEQ linear phase EQ plugin

Full-featured linear phase EQ with interactive graphical curve display.
FIR-based processing (8192-tap), 8 parametric bands, multi-platform
CI/CD (Windows/macOS/Linux), InstaDrums visual style.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Source/EQBand.h

@@ -0,0 +1,12 @@
+#pragma once
+
+struct EQBand
+{
+    enum Type { Peak, LowShelf, HighShelf };
+
+    float frequency = 1000.0f;  // 20 Hz - 20000 Hz
+    float gainDb    = 0.0f;     // -24 dB to +24 dB
+    float q         = 1.0f;     // 0.1 to 18.0
+    Type  type      = Peak;
+    bool  enabled   = true;
+};