feat: add C++ support with ImGui/ImPlot framework and vendor submodules

Añade soporte C++ al registry: vendor submodules (glfw, imgui, implot, tracy),
sistema de build con CMake y toolchains cross-platform, runner C++ en fn CLI,
parser de tests Google Test, y funciones bash para build Linux/Windows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bash/functions/infra/build_cpp_windows.sh

@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+REGISTRY_ROOT="${FN_REGISTRY_ROOT:-$(cd "$(dirname "$0")/../../.." && pwd)}"
+CPP_ROOT="$REGISTRY_ROOT/cpp"
+BUILD_DIR="$CPP_ROOT/build/windows"
+TOOLCHAIN="$CPP_ROOT/toolchains/mingw-w64.cmake"
+TARGET="${1:-}"
+
+# Check mingw is available
+if ! command -v x86_64-w64-mingw32-g++ &>/dev/null; then
+    echo "[build_cpp_windows] Error: mingw-w64 not found. Install with: sudo apt install mingw-w64"
+    exit 1
+fi
+
+# Configure if needed
+if [ ! -f "$BUILD_DIR/CMakeCache.txt" ]; then
+    echo "[build_cpp_windows] Configuring cmake with mingw-w64 toolchain..."
+    cmake -B "$BUILD_DIR" -S "$CPP_ROOT" -DCMAKE_TOOLCHAIN_FILE="$TOOLCHAIN"
+fi
+
+# Build
+if [ -n "$TARGET" ]; then
+    echo "[build_cpp_windows] Cross-compiling target: $TARGET"
+    cmake --build "$BUILD_DIR" --target "$TARGET" -- -j"$(nproc)"
+else
+    echo "[build_cpp_windows] Cross-compiling all targets..."
+    cmake --build "$BUILD_DIR" -- -j"$(nproc)"
+fi
+
+echo "[build_cpp_windows] Done. Windows binaries in $BUILD_DIR"
+if [ -n "$TARGET" ]; then
+    file "$BUILD_DIR"/**/"$TARGET".exe 2>/dev/null || file "$BUILD_DIR/$TARGET".exe 2>/dev/null || true
+fi