add calculator build

wasm/bindings/calculator_embind.cpp

@@ -0,0 +1,18 @@
+/*
+ * Embind bindings for KiCad PCB Calculator WASM.
+ *
+ * Currently empty — reserved for future calculator-specific JS bindings
+ * (e.g., exposing transmission-line calculators or attenuator math to
+ * Pyodide / browser callers). Kept as a separate translation unit so the
+ * calculator build pipeline mirrors pcbnew's pcbnew_embind.cpp structure.
+ */
+
+#ifdef __EMSCRIPTEN__
+#include <emscripten/bind.h>
+
+using namespace emscripten;
+
+EMSCRIPTEN_BINDINGS(pcb_calculator) {
+    // Reserved for future calculator-specific JS bindings.
+}
+#endif