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_linux.md

@@ -0,0 +1,36 @@
+---
+name: build_cpp_linux
+kind: function
+lang: bash
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "build_cpp_linux(target?: string) -> void"
+description: "Compila las funciones y apps C++ del registry para Linux nativo usando cmake"
+tags: [cpp, build, cmake, linux, 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_linux.sh"
+params:
+  - name: target
+    desc: "Nombre del target cmake a compilar (opcional, sin argumento compila todo)"
+output: "Compila los binarios en cpp/build/linux/"
+---
+
+# build_cpp_linux
+
+Configura y compila el proyecto C++ (ImGui/ImPlot) para Linux nativo.
+
+Usa cmake con compilacion paralela (`-j$(nproc)`). Si no se ha configurado antes, ejecuta `cmake -B` automaticamente.
+
+```bash
+fn run build_cpp_linux              # Compilar todo
+fn run build_cpp_linux chart_demo   # Compilar solo chart_demo
+```