feat(webgl): Fix GL initialization and add GLSL ES shader conversion

Progress on WEBGL_GAL rendering:

- Fix GLImmediateShim initialization by adding GL function dependencies
  (glBegin, glEnd, glVertex2f, etc.) to $GLImmediateShim__deps
- Add COLOR4D(EDA_COLOR_T) constructor stub to wasm_stubs.cpp
- Fix GAL context locking - add LockContext/UnlockContext calls
- Add exception catching to build (-sNO_DISABLE_EXCEPTION_CATCHING)
- Create GLSL ES 1.00 shader converter in generate_shaders.py:
  - Remove #version 120 directive (ES 1.00 default)
  - Add precision highp float/int qualifiers
  - Convert int * float to float literals (2 * x -> 2.0 * x)
- Update build script to clean output files for linker flag changes
- Add console capture to test spec for debugging

Current status:
- WASM builds and loads successfully
- GLImmediateShim initializes correctly
- WEBGL_GAL creates successfully
- Shader compilation fails due to Emscripten LEGACY_GL_EMULATION
  prepending code that conflicts with custom shader precision

Next: Investigate shader compilation with LEGACY_GL_EMULATION or
consider alternative approaches for GL compatibility.

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

tests/gal-regression/wasm/Makefile

@@ -61,13 +61,15 @@ CXXFLAGS = $(OPT_FLAGS) $(WX_CXXFLAGS) $(KICAD_INCLUDES) -std=c++20
 # Emscripten flags
 BASE_LDFLAGS = -sALLOW_MEMORY_GROWTH=1 \
                -sERROR_ON_UNDEFINED_SYMBOLS=0 \
+               -sNO_DISABLE_EXCEPTION_CATCHING \
                -sEXPORTED_FUNCTIONS=['_main','_runScenario','_getTotalScenarios','_getCurrentScenario','_getCanvasWidth','_getCanvasHeight'] \
                -sEXPORTED_RUNTIME_METHODS=['ccall','cwrap','HEAPU8'] \
                -sMODULARIZE=1 \
                -sEXPORT_NAME='createGALTest' \
                -sENVIRONMENT=web
 
-# GL-specific flags - LEGACY_GL_EMULATION handles legacy GL calls
+# GL-specific flags - LEGACY_GL_EMULATION handles legacy GL calls (glBegin/glEnd)
+# WebGL 2.0 for modern shader support
 EM_GL_FLAGS = -sLEGACY_GL_EMULATION=1 -sMAX_WEBGL_VERSION=2
 GL_SHIM = $(PROJECT_ROOT)/wasm/shims/gl_immediate_shim.js