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/FindZLIB.cmake

@@ -0,0 +1,38 @@
+# FindZLIB.cmake - WASM builds use Emscripten's zlib port
+# Emscripten provides zlib via -sUSE_ZLIB=1 flag
+
+if(EMSCRIPTEN)
+    message(STATUS "Using Emscripten's zlib port (-sUSE_ZLIB=1)")
+
+    # Find the Emscripten cache sysroot
+    execute_process(
+        COMMAND em-config CACHE
+        OUTPUT_VARIABLE EMSCRIPTEN_CACHE
+        OUTPUT_STRIP_TRAILING_WHITESPACE
+    )
+
+    # Set ZLIB variables
+    set(ZLIB_FOUND TRUE)
+    set(ZLIB_INCLUDE_DIR "${EMSCRIPTEN_CACHE}/sysroot/include")
+    set(ZLIB_INCLUDE_DIRS "${ZLIB_INCLUDE_DIR}")
+
+    # The library will be linked via -sUSE_ZLIB=1
+    # We set a placeholder for CMake checks
+    set(ZLIB_LIBRARY "-sUSE_ZLIB=1")
+    set(ZLIB_LIBRARIES "-sUSE_ZLIB=1")
+    set(ZLIB_VERSION_STRING "1.3.1")
+
+    # Create imported target
+    if(NOT TARGET ZLIB::ZLIB)
+        add_library(ZLIB::ZLIB INTERFACE IMPORTED)
+        set_target_properties(ZLIB::ZLIB PROPERTIES
+            INTERFACE_INCLUDE_DIRECTORIES "${ZLIB_INCLUDE_DIR}"
+            INTERFACE_LINK_LIBRARIES "-sUSE_ZLIB=1"
+        )
+    endif()
+
+    mark_as_advanced(ZLIB_INCLUDE_DIR ZLIB_LIBRARY)
+else()
+    # For non-WASM builds, use the system FindZLIB
+    include(${CMAKE_ROOT}/Modules/FindZLIB.cmake OPTIONAL)
+endif()