Add KiCad PCBnew WASM build support and documentation

Build infrastructure:
- Update build-pcbnew.sh with stub library compilation
- Update build-wxuniversal-wasm.sh with library symlinks and stubs
- Add stub libraries for libgit2 and curl (network ops via JS)
- Add WASM-specific CMake Find modules

Documentation:
- Add KICAD_WASM_BUILD.md with complete modification list
- Document 68 KiCad files modified for WASM support
- Document disabled features and reasons
- Document stub libraries and wxWidgets changes

Submodule updates:
- kicad: Add WASM/Emscripten build support (wasm-port branch)
- wxwidgets: Add KiCad compatibility fixes

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

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

wasm/kiplatform/printing.cpp

@@ -0,0 +1,22 @@
+/*
+ * WASM implementation of printing.h
+ * Printing is not directly supported in browser environment
+ */
+
+#include <printing.h>
+#include <string>
+
+namespace KIPLATFORM
+{
+namespace PRINTING
+{
+
+PRINT_RESULT PrintPDF( const std::string& aFile )
+{
+    // Direct printing is not supported in browser
+    // User can use browser's print functionality or download the PDF
+    return PRINT_RESULT::UNSUPPORTED;
+}
+
+} // namespace PRINTING
+} // namespace KIPLATFORM