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/cmake/Findnng.cmake

@@ -0,0 +1,41 @@
+# Findnng.cmake - Stub for WASM builds
+# nng (NanoMsg Next Gen) is used for IPC in KiCad
+# For WASM builds, we stub this out as IPC works differently in the browser
+
+if(EMSCRIPTEN)
+    message(STATUS "nng stubbed for WASM build (IPC handled differently in browser)")
+
+    # Set variables to indicate nng is "found" (stubbed)
+    set(NNG_FOUND TRUE)
+    set(nng_FOUND TRUE)
+    set(NNG_LIBRARY "")
+    set(NNG_LIBRARIES "")
+    set(NNG_INCLUDE_DIR "")
+    set(NNG_INCLUDE_DIRS "")
+
+    # Create an imported target for nng
+    if(NOT TARGET nng::nng)
+        add_library(nng::nng INTERFACE IMPORTED)
+    endif()
+
+    mark_as_advanced(
+        NNG_FOUND
+        NNG_LIBRARY
+        NNG_INCLUDE_DIR
+    )
+else()
+    # For non-WASM builds, use the system Findnng or search for it
+    find_path(NNG_INCLUDE_DIR nng/nng.h)
+    find_library(NNG_LIBRARY NAMES nng)
+
+    include(FindPackageHandleStandardArgs)
+    find_package_handle_standard_args(nng DEFAULT_MSG NNG_LIBRARY NNG_INCLUDE_DIR)
+
+    if(NNG_FOUND AND NOT TARGET nng::nng)
+        add_library(nng::nng UNKNOWN IMPORTED)
+        set_target_properties(nng::nng PROPERTIES
+            IMPORTED_LOCATION "${NNG_LIBRARY}"
+            INTERFACE_INCLUDE_DIRECTORIES "${NNG_INCLUDE_DIR}"
+        )
+    endif()
+endif()