afegit suport Emscripten/WebAssembly al build system (milestone 4)

- createSystemFolder() adaptat per Emscripten (MEMFS, sense pwd.h/unistd.h)
- initOptions() amb windowSize=1 i videoMode=0 per Emscripten
- CMakeLists.txt: SDL3 via FetchContent per Emscripten, --preload-file data
- Makefile: target wasm amb Docker (emscripten/emsdk)
- Build de Linux verificat, segueix funcionant correctament

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Makefile

@@ -236,6 +236,18 @@ linux_release:
 # Elimina la carpeta temporal
 	$(RMDIR) "$(RELEASE_FOLDER)"
 
+# ==============================================================================
+# COMPILACIÓN PARA WEBASSEMBLY (requiere Docker)
+# ==============================================================================
+wasm:
+	@echo "Compilando para WebAssembly - Version: $(VERSION)"
+	docker run --rm \
+		-v $(DIR_ROOT):/src \
+		-w /src \
+		emscripten/emsdk:latest \
+		bash -c "emcmake cmake -S . -B build_wasm -DCMAKE_BUILD_TYPE=Release && cmake --build build_wasm"
+	@echo "Output: build_wasm/coffee_crisis.html, .js, .wasm, .data"
+
 # ==============================================================================
 # REGLAS ESPECIALES
 # ==============================================================================
@@ -255,9 +267,10 @@ help:
 	@echo "    make windows_release - Crear release para Windows"
 	@echo "    make linux_release   - Crear release para Linux"
 	@echo "    make macos_release   - Crear release para macOS"
+	@echo "    make wasm            - Compilar para WebAssembly (requiere Docker)"
 	@echo ""
 	@echo "  Otros:"
 	@echo "    make show_version    - Mostrar version actual ($(VERSION))"
 	@echo "    make help            - Mostrar esta ayuda"
 
-.PHONY: all debug release windows_release macos_release linux_release show_version help
+.PHONY: all debug release windows_release macos_release linux_release wasm show_version help