Complete Phase 1: Build KiCad with optional dependencies disabled

Add CMake override modules, stub implementations, and patches to build
KiCad without CURL, libgit2, OpenCASCADE, and ngspice dependencies.

- cmake/: Find modules that provide stub targets when deps disabled
- stubs/include/: Header stubs for curl, git2, ngspice, OCC
- stubs/src/: Implementation stubs for disabled features
- patches/: Consolidated patch for KiCad source modifications
- scripts/: Build helper scripts

Verified full native build on macOS with all optional deps disabled.

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

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

cmake/Findngspice.cmake

@@ -0,0 +1,56 @@
+#
+# KiCad Wasm Port - ngspice Find Module Override
+#
+# When KICAD_USE_NGSPICE=OFF, this module provides stub values
+# so the build can proceed without ngspice.
+#
+
+# Check if ngspice is disabled
+if(DEFINED KICAD_USE_NGSPICE AND NOT KICAD_USE_NGSPICE)
+    message(STATUS "ngspice: DISABLED (KICAD_USE_NGSPICE=OFF)")
+
+    # Set stubs include directory
+    set(STUBS_INCLUDE_DIR "${CMAKE_CURRENT_LIST_DIR}/../stubs/include")
+
+    # Set variables that KiCad expects
+    # ngspice is dynamically loaded via dlopen, so we don't need to link against it.
+    # Set library variables to empty to prevent linking.
+    set(ngspice_FOUND TRUE)
+    set(NGSPICE_FOUND TRUE)
+    set(NGSPICE_INCLUDE_DIR "${STUBS_INCLUDE_DIR}")
+    set(NGSPICE_INCLUDE_DIRS "${STUBS_INCLUDE_DIR}")
+    # Empty library - ngspice is loaded dynamically, not linked
+    set(NGSPICE_LIBRARY "" CACHE STRING "ngspice library (disabled)")
+    set(NGSPICE_LIBRARIES "")
+    set(NGSPICE_VERSION "disabled")
+    # NGSPICE_DLL is used by eeschema at runtime, not link time
+    set(NGSPICE_DLL "")
+
+    # Add stub includes globally
+    include_directories("${STUBS_INCLUDE_DIR}")
+
+    return()
+endif()
+
+# Otherwise, use the original find module from KiCad
+list(REMOVE_ITEM CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
+
+set(_KICAD_CMAKE_DIR "${CMAKE_SOURCE_DIR}/cmake")
+if(EXISTS "${_KICAD_CMAKE_DIR}/Findngspice.cmake")
+    include("${_KICAD_CMAKE_DIR}/Findngspice.cmake")
+else()
+    # Fallback search
+    find_path(NGSPICE_INCLUDE_DIR NAMES ngspice/sharedspice.h)
+    find_library(NGSPICE_LIBRARY NAMES ngspice)
+
+    include(FindPackageHandleStandardArgs)
+    find_package_handle_standard_args(ngspice DEFAULT_MSG
+        NGSPICE_LIBRARY NGSPICE_INCLUDE_DIR)
+
+    set(NGSPICE_LIBRARIES ${NGSPICE_LIBRARY})
+    set(NGSPICE_INCLUDE_DIRS ${NGSPICE_INCLUDE_DIR})
+
+    mark_as_advanced(NGSPICE_INCLUDE_DIR NGSPICE_LIBRARY)
+endif()
+
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")