feat(webgl): Add GAL native test harness for visual regression testing

Add a standalone test application that compiles KiCad's actual OPENGL_GAL
against system wxWidgets to generate baseline screenshots for comparing
native OpenGL rendering against WebGL rendering in the browser.

Architecture:
- Compiles 18 KiCad GAL source files from the kicad submodule
- Uses template-based private member accessor (safer than #define private public)
- Generates shader C++ files from GLSL (10 shader pairs for SMAA AA)
- Minimal stubs for KiCad dependencies (PGM_BASE, ADVANCED_CFG, etc.)

Test coverage:
- 11 scenarios testing ~19% of GAL API
- basic-lines, line-widths, circles, arcs, rectangles, polygons
- alpha-blending, transforms, grid-cursor, segments, complex-scene

Key insights documented:
- GAL uses world-to-screen transformation requiring 1:1 pixel mapping
- FBO reading required for clean screenshots on macOS
- Layer depth needed for proper z-ordering in complex scenes

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/gal-regression/native/config.h

@@ -0,0 +1,26 @@
+// Minimal config.h for native GAL test
+// Based on KiCad's generated config
+#ifndef KICAD_CONFIG_H
+#define KICAD_CONFIG_H
+
+// Version info
+#define KICAD_MAJOR_VERSION 8
+#define KICAD_MINOR_VERSION 0
+#define KICAD_PATCH_VERSION 0
+
+// Enable OpenGL
+#define KICAD_USE_OCC 0
+#define KICAD_USE_EGL 0
+
+// Platform detection
+#ifdef __APPLE__
+#define KICAD_MACOS 1
+#endif
+
+// Math
+#define KICAD_USE_STDROUND 1
+
+// Ensure types are properly sized
+#include <cstdint>
+
+#endif // KICAD_CONFIG_H