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/UsewxWidgets.cmake

@@ -0,0 +1,24 @@
+# UsewxWidgets.cmake - WASM build version
+# This file is included after FindwxWidgets to set up wxWidgets for the build
+
+if(wxWidgets_FOUND)
+    # Add include directories
+    if(wxWidgets_INCLUDE_DIRS)
+        include_directories(SYSTEM ${wxWidgets_INCLUDE_DIRS})
+    endif()
+
+    # Add library directories
+    if(wxWidgets_LIBRARY_DIRS)
+        link_directories(${wxWidgets_LIBRARY_DIRS})
+    endif()
+
+    # Add definitions
+    if(wxWidgets_DEFINITIONS)
+        add_definitions(${wxWidgets_DEFINITIONS})
+    endif()
+
+    # Add compiler flags
+    if(wxWidgets_CXX_FLAGS)
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${wxWidgets_CXX_FLAGS}")
+    endif()
+endif()