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/secrets.cpp

@@ -0,0 +1,76 @@
+/*
+ * WASM implementation of kiplatform/secrets.h
+ * Uses browser localStorage for basic secret storage
+ * Note: localStorage is NOT secure for sensitive secrets, but provides
+ * the same API for KiCad functionality that expects secret storage
+ */
+
+#include <kiplatform/secrets.h>
+#include <wx/string.h>
+
+#ifdef __EMSCRIPTEN__
+#include <emscripten.h>
+#endif
+
+namespace KIPLATFORM
+{
+namespace SECRETS
+{
+
+bool StoreSecret( const wxString& aService, const wxString& aKey, const wxString& aSecret )
+{
+#ifdef __EMSCRIPTEN__
+    int result = EM_ASM_INT({
+        try {
+            var service = UTF8ToString($0);
+            var key = UTF8ToString($1);
+            var secret = UTF8ToString($2);
+            var storageKey = 'kicad_secret_' + service + '_' + key;
+            localStorage.setItem(storageKey, secret);
+            return 1;
+        } catch(e) {
+            console.warn('Failed to store secret:', e);
+            return 0;
+        }
+    }, aService.utf8_str().data(), aKey.utf8_str().data(), aSecret.utf8_str().data());
+    return result == 1;
+#else
+    return false;
+#endif
+}
+
+bool GetSecret( const wxString& aService, const wxString& aKey, wxString& aSecret )
+{
+#ifdef __EMSCRIPTEN__
+    char* result = (char*)EM_ASM_PTR({
+        try {
+            var service = UTF8ToString($0);
+            var key = UTF8ToString($1);
+            var storageKey = 'kicad_secret_' + service + '_' + key;
+            var secret = localStorage.getItem(storageKey);
+            if (secret === null) {
+                return 0;
+            }
+            var len = lengthBytesUTF8(secret) + 1;
+            var buf = _malloc(len);
+            stringToUTF8(secret, buf, len);
+            return buf;
+        } catch(e) {
+            console.warn('Failed to get secret:', e);
+            return 0;
+        }
+    }, aService.utf8_str().data(), aKey.utf8_str().data());
+
+    if (result) {
+        aSecret = wxString::FromUTF8(result);
+        free(result);
+        return true;
+    }
+    return false;
+#else
+    return false;
+#endif
+}
+
+} // namespace SECRETS
+} // namespace KIPLATFORM