Adds the platform layer for building whoa as a WebAssembly application:
Working:
- CMake configuration for WHOA_SYSTEM_WEB with pthreads and ASYNCIFY
- Web entry point and HTML shell template
- Event loop adapted for emscripten_set_main_loop callback model
- WebSocket-based networking (WowConnection over JS WebSocket API)
- Sound system stubs (audio not yet implemented)
- FetchFS for async file loading from web server
- Freetype fixes for WASM compatibility (type mismatches)
- Input handling for web canvas
Missing (in separate commits):
- WebGPU graphics backend (CGxDeviceWebGPU)
- WGSL shaders
- API selection in Device.cpp
