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.md

@@ -0,0 +1,38 @@
+---
+name: build_cpp_windows
+kind: function
+lang: bash
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "build_cpp_windows(target?: string) -> void"
+description: "Cross-compila las funciones y apps C++ del registry para Windows usando mingw-w64"
+tags: [cpp, build, cmake, windows, cross-compile, mingw, imgui]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: []
+tested: false
+tests: []
+test_file_path: ""
+file_path: "bash/functions/infra/build_cpp_windows.sh"
+params:
+  - name: target
+    desc: "Nombre del target cmake a compilar (opcional, sin argumento compila todo)"
+output: "Produce binarios .exe de Windows en cpp/build/windows/"
+---
+
+# build_cpp_windows
+
+Cross-compila el proyecto C++ para Windows desde Linux usando el toolchain mingw-w64.
+
+Los .exe resultantes incluyen runtime linkado estaticamente (self-contained).
+
+```bash
+fn run build_cpp_windows              # Compilar todo
+fn run build_cpp_windows chart_demo   # Compilar solo chart_demo
+```
+
+Requiere `mingw-w64`: `sudo apt install mingw-w64`