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/Findlibgit2.cmake

@@ -0,0 +1,64 @@
+#
+# KiCad Wasm Port - libgit2 Find Module Override
+#
+# When KICAD_USE_GIT=OFF, this module provides stub values
+# so the build can proceed without libgit2.
+#
+
+# Check if git is disabled
+if(DEFINED KICAD_USE_GIT AND NOT KICAD_USE_GIT)
+    message(STATUS "libgit2: DISABLED (KICAD_USE_GIT=OFF)")
+
+    # Set variables that KiCad expects
+    set(LIBGIT2_FOUND TRUE)
+    set(LIBGIT2_INCLUDE_DIR "")
+    set(LIBGIT2_INCLUDE_DIRS "")
+    set(LIBGIT2_LIBRARIES "")
+    set(LIBGIT2_DEFINITIONS "")
+    set(LIBGIT2_VERSION_STRING "stub")
+
+    # Mark as found
+    set(libgit2_FOUND TRUE)
+
+    return()
+endif()
+
+# Otherwise, use the original find module from KiCad
+# First, remove our cmake dir from the module path to avoid recursion
+list(REMOVE_ITEM CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
+
+# Look for the original module in KiCad's cmake dir
+set(_KICAD_CMAKE_DIR "${CMAKE_SOURCE_DIR}/cmake")
+if(EXISTS "${_KICAD_CMAKE_DIR}/Findlibgit2.cmake")
+    include("${_KICAD_CMAKE_DIR}/Findlibgit2.cmake")
+else()
+    # Fallback: Use pkg-config
+    find_package(PkgConfig)
+    pkg_search_module(PC_LIBGIT2 libgit2)
+
+    set(LIBGIT2_DEFINITIONS ${PC_LIBGIT2_CFLAGS_OTHER})
+
+    find_path(LIBGIT2_INCLUDE_DIR NAMES git2.h
+        HINTS
+        ${PC_LIBGIT2_INCLUDEDIR}
+        ${PC_LIBGIT2_INCLUDE_DIRS}
+    )
+
+    find_library(LIBGIT2_LIBRARY NAMES git2
+        HINTS
+        ${PC_LIBGIT2_LIBDIR}
+        ${PC_LIBGIT2_LIBRARY_DIRS}
+    )
+
+    set(LIBGIT2_LIBRARIES ${LIBGIT2_LIBRARY})
+    set(LIBGIT2_INCLUDE_DIRS ${LIBGIT2_INCLUDE_DIR})
+
+    include(FindPackageHandleStandardArgs)
+    find_package_handle_standard_args(libgit2 DEFAULT_MSG
+        LIBGIT2_LIBRARY LIBGIT2_INCLUDE_DIR)
+
+    mark_as_advanced(LIBGIT2_INCLUDE_DIR LIBGIT2_LIBRARY)
+endif()
+
+# Restore module path
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")