Enable exceptions and pthreads atomics for KiCad WASM build

Build fixes:
- Enable C++ exceptions in wxWidgets (--enable-exceptions, -fexceptions)
  Required for KiCad's OnExceptionInMainLoop override in debug builds
- Add -matomics -mbulk-memory to all dependency builds for shared memory
  Required for pthreads support with Emscripten
- Fix docker/build.sh output copy path (pcbnew/ not bin/)
- Make workspace mount read-only in docker-compose.yml

Updated dependency scripts:
- build-freetype.sh, build-harfbuzz.sh, build-protobuf.sh
- build-zstd.sh, build-opencascade.sh, build-boost.sh
- build-pixman.sh, build-cairo.sh (meson cross-file)
- build-wxuniversal-wasm.sh, build-pcbnew.sh

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

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

docker/build.sh

@@ -14,6 +14,6 @@ docker compose -f docker/docker-compose.yml exec kicad-wasm-builder \
 # Copy output to host-accessible directory
 echo "Copying build output to ./output/..."
 docker compose -f docker/docker-compose.yml exec kicad-wasm-builder \
-    bash -c "mkdir -p /workspace/output && cp -r /workspace/build-wasm/kicad-pcbnew/bin/* /workspace/output/ 2>/dev/null || true"
+    bash -c "mkdir -p /workspace/output && cp /workspace/build-wasm/kicad-pcbnew/pcbnew/pcbnew.{js,wasm,wasm.map,worker.js} /workspace/output/ 2>/dev/null || cp /workspace/build-wasm/kicad-pcbnew/pcbnew/pcbnew.{js,wasm} /workspace/output/"
 
 echo "Build complete. Output files in ./output/"