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>

.gitmodules

@@ -0,0 +1,13 @@
+[submodule "cpp/vendor/imgui"]
+	path = cpp/vendor/imgui
+	url = https://github.com/ocornut/imgui.git
+	branch = docking
+[submodule "cpp/vendor/implot"]
+	path = cpp/vendor/implot
+	url = https://github.com/epezent/implot.git
+[submodule "cpp/vendor/tracy"]
+	path = cpp/vendor/tracy
+	url = https://github.com/wolfpld/tracy.git
+[submodule "/home/lucas/fn_registry/cpp/vendor/glfw"]
+	path = /home/lucas/fn_registry/cpp/vendor/glfw
+	url = https://github.com/glfw/glfw.git