feat: add multi-viewport support and SQLite amalgamation to C++ framework

- AppConfig.viewports flag para ventanas OS reales fuera del main window
- Multi-viewport render loop en app_base.cpp (UpdatePlatformWindows)
- SQLite amalgamation vendoreada para Windows cross-compile
- LANGUAGES C CXX en CMakeLists para compilar sqlite3.c
- Fix pie_chart.cpp para nueva API de ImPlot (PlotPieChart sin flags arg)
- imgui.ini añadido a gitignore

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

cpp/framework/app_base.h

@@ -9,6 +9,7 @@ struct AppConfig {
     int width = 1280;
     int height = 720;
     bool vsync = true;
+    bool viewports = false; // Enable multi-viewport: ImGui windows become real OS windows
     float bg_r = 0.1f;
     float bg_g = 0.1f;
     float bg_b = 0.1f;