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>

scripts/build-gal-webgl-test.sh

@@ -57,6 +57,10 @@ if [ "$CLEAN_BUILD" = "1" ]; then
     make clean 2>/dev/null || true
 fi
 
+# Always remove output files to ensure linker flags changes take effect
+# (Makefile only tracks object file dependencies, not linker flag changes)
+rm -f "$OUTPUT_DIR"/*.js "$OUTPUT_DIR"/*.wasm 2>/dev/null || true
+
 echo ""
 echo "Building..."
 if [ "$DEBUG_BUILD" = "1" ]; then