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/CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.16)
-project(fn_registry_cpp LANGUAGES CXX)
+project(fn_registry_cpp LANGUAGES C CXX)
 
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
@@ -98,3 +98,8 @@ endfunction()
 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/apps/chart_demo/CMakeLists.txt)
     add_subdirectory(apps/chart_demo)
 endif()
+
+# --- Registry Dashboard (lives in apps/ per project convention) ---
+if(EXISTS ${CMAKE_SOURCE_DIR}/../apps/registry_dashboard/CMakeLists.txt)
+    add_subdirectory(${CMAKE_SOURCE_DIR}/../apps/registry_dashboard ${CMAKE_BINARY_DIR}/apps/registry_dashboard)
+endif()