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>

stubs/include/curl/easy.h

@@ -0,0 +1,12 @@
+/*
+ * KiCad Wasm Port - CURL Easy API Stub Header
+ *
+ * This stub is empty because curl.h includes all the easy API.
+ */
+
+#ifndef KICAD_WASM_CURL_EASY_STUB_H
+#define KICAD_WASM_CURL_EASY_STUB_H
+
+#include "curl.h"
+
+#endif /* KICAD_WASM_CURL_EASY_STUB_H */