Add KiCad WASM build infrastructure and dependency scripts

- Add build environment setup (scripts/common/env.sh, versions.sh, functions.sh)
- Add dependency build scripts for Zstd, GLM, FreeType, HarfBuzz, Pixman, Cairo
- Add placeholder scripts for OpenCASCADE, ngspice, protobuf
- Add WASM compatibility layer (wasm/kiplatform/, wasm/libcontext/)
- Add CMake modules for KiCad WASM cross-compilation
- Add PCBnew test infrastructure (tests/kicad/)
- Add build plan documentation

Successfully tested builds: Zstd 1.5.5, GLM 0.9.9.8, FreeType 2.13.2,
HarfBuzz 8.3.0, Pixman 0.42.2, Cairo 1.18.0

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

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

wasm/kiplatform/io.cpp

@@ -0,0 +1,49 @@
+/*
+ * WASM implementation of kiplatform/io.h
+ * Provides file I/O functions for WASM virtual filesystem
+ */
+
+#include <kiplatform/io.h>
+#include <wx/string.h>
+#include <wx/filename.h>
+#include <stdio.h>
+
+namespace KIPLATFORM
+{
+namespace IO
+{
+
+FILE* SeqFOpen( const wxString& aPath, const wxString& mode )
+{
+    // WASM doesn't have special sequential read hints
+    // Just use standard fopen
+    return fopen( aPath.utf8_str(), mode.utf8_str() );
+}
+
+bool DuplicatePermissions( const wxString& aSrc, const wxString& aDest )
+{
+    // WASM virtual filesystem doesn't have detailed permissions
+    return true;
+}
+
+bool MakeWriteable( const wxString& aFilePath )
+{
+    // All files in WASM virtual filesystem are writeable
+    return true;
+}
+
+bool IsFileHidden( const wxString& aFileName )
+{
+    // Check for Unix-style hidden files (starting with .)
+    wxFileName fn( aFileName );
+    wxString name = fn.GetFullName();
+    return !name.IsEmpty() && name[0] == '.';
+}
+
+void LongPathAdjustment( wxFileName& aFilename )
+{
+    // No-op on non-Windows platforms
+}
+
+} // namespace IO
+} // namespace KIPLATFORM