feat(webgl): Add 4 new GAL test scenarios for expanded coverage

Expand test coverage from ~19% to ~25% of GAL API with modular scenario files:
- bezier-curves: Tests DrawCurve() with S-curves, waves, hearts, and control points
- arc-segments: Tests DrawArcSegment() with thick arc strokes (PCB trace style)
- segment-chain: Tests DrawSegmentChain() with zigzags, spirals, sharp corners
- group-caching: Tests BeginGroup/EndGroup/DrawGroup for cached geometry

Architecture:
- New scenarios in separate files under scenarios/
- Forward declarations in main gal_test_scenarios.cpp
- CMakeLists.txt updated to compile new scenario modules

Also:
- Remove unused build-wxwidgets-native.sh (using system wxWidgets)

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

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

tests/gal-regression/native/CMakeLists.txt

@@ -62,13 +62,23 @@ set(KICAD_GAL_SOURCES
 set(STUB_SOURCES
     ${CMAKE_SOURCE_DIR}/kicad_stubs.cpp
     ${CMAKE_SOURCE_DIR}/gal_test_accessor.cpp
+)
+
+# Test scenario files
+set(SCENARIO_SOURCES
     ${CMAKE_SOURCE_DIR}/../scenarios/gal_test_scenarios.cpp
+    # New modular scenarios
+    ${CMAKE_SOURCE_DIR}/../scenarios/scenario_bezier_curves.cpp
+    ${CMAKE_SOURCE_DIR}/../scenarios/scenario_arc_segments.cpp
+    ${CMAKE_SOURCE_DIR}/../scenarios/scenario_segment_chain.cpp
+    ${CMAKE_SOURCE_DIR}/../scenarios/scenario_group_caching.cpp
 )
 
 # Main executable
 add_executable(gal_native_test
     gal_native_test.cpp
     ${STUB_SOURCES}
+    ${SCENARIO_SOURCES}
     ${KICAD_GAL_SOURCES}
     ${SHADER_SOURCES}
 )