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/trace_helpers.h

@@ -0,0 +1,66 @@
+// Stub trace_helpers.h for native GAL test
+// Provides simplified TRACE_MANAGER that doesn't use wxWidgets macros
+
+#ifndef TRACE_HELPERS_H_STUB
+#define TRACE_HELPERS_H_STUB
+
+#include <wx/wx.h>
+#include <map>
+#include <cstdarg>
+
+// Forward declaration
+class wxArrayString;
+
+// Trace channel names (extern declarations)
+extern const wxString traceGalProfile;
+extern const wxString traceOpenGL;
+extern const wxString traceGalCachedContainer;
+extern const wxString traceShader;
+
+// Definitions
+inline const wxString traceGalProfile = "KICAD_GAL_PROFILE";
+inline const wxString traceOpenGL = "KICAD_OPENGL";
+inline const wxString traceGalCachedContainer = "KICAD_GAL_CACHED_CONTAINER";
+inline const wxString traceShader = "KICAD_SHADER";
+
+// TRACE_MANAGER - simplified stub
+class TRACE_MANAGER {
+public:
+    TRACE_MANAGER() : m_globalTraceEnabled(false), m_printAllTraces(false) {}
+    ~TRACE_MANAGER() {}
+
+    static TRACE_MANAGER& Instance() {
+        static TRACE_MANAGER instance;
+        return instance;
+    }
+
+    // Trace methods - variadic template version
+    template<typename... Args>
+    void Trace(const wxString&, Args...) {
+        // No-op - tracing disabled for test
+    }
+
+    // wxWidgets-style methods for compatibility
+    void DoTrace(const wxString&, const char*, ...) {}
+    void DoTraceUtf8(const wxString&, const char*, ...) {}
+
+    bool IsTraceEnabled(const wxString&) const {
+        return false;  // Always disabled for test
+    }
+
+private:
+    std::map<wxString, bool> m_enabledTraces;
+    bool m_globalTraceEnabled;
+    bool m_printAllTraces;
+};
+
+// KI_TRACE macro - no-op since IsTraceEnabled always returns false
+#define KI_TRACE(aWhat, ...) \
+    if (TRACE_MANAGER::Instance().IsTraceEnabled(aWhat)) { \
+        TRACE_MANAGER::Instance().Trace(aWhat, __VA_ARGS__); \
+    }
+
+// Dump function stub
+inline wxString dump(const wxArrayString&) { return wxString(); }
+
+#endif // TRACE_HELPERS_H_STUB