feat(cpp): integrar Catch2 en CMake con BUILD_TESTING + add_fn_test helper

cpp/tests/CMakeLists.txt compila Catch2 amalgamated como STATIC libreria
una sola vez. Cada test es su propio executable (CATCH_CONFIG_MAIN por
archivo) y se registra con add_test(). add_fn_test(name srcs...) es el
helper: incluye paths de cpp/functions y cpp/framework, linka catch2.

Tests que necesitan symbols reales (fn_framework, imgui) los anaden
explicitamente con target_link_libraries despues.

cpp/CMakeLists.txt

@@ -199,3 +199,10 @@ set(_DASH_DIR ${CMAKE_SOURCE_DIR}/../projects/fn_monitoring/apps/registry_dashbo
 if(EXISTS ${_DASH_DIR}/CMakeLists.txt)
     add_subdirectory(${_DASH_DIR} ${CMAKE_BINARY_DIR}/apps/registry_dashboard)
 endif()
+
+# --- Tests (Catch2 amalgamated, ctest-driven) ---
+option(BUILD_TESTING "Build C++ tests" ON)
+if(BUILD_TESTING)
+    enable_testing()
+    add_subdirectory(tests)
+endif()

cpp/tests/CMakeLists.txt

@@ -0,0 +1,53 @@
+# cpp/tests — Catch2 unit tests for primitives.
+#
+# Catch2 amalgamated is compiled once as a STATIC LIB. Each test binary is
+# its own executable so we can mix tests that use ImGui-context and tests
+# that are pure logic without polluting symbols.
+
+add_library(catch2 STATIC
+    ${CMAKE_CURRENT_SOURCE_DIR}/../vendor/catch2/catch_amalgamated.cpp)
+target_include_directories(catch2 PUBLIC
+    ${CMAKE_CURRENT_SOURCE_DIR}/../vendor/catch2)
+target_compile_features(catch2 PUBLIC cxx_std_17)
+
+# Helper: register a test executable.
+#   add_fn_test(<name> <sources...>)
+# By default links Catch2 + the cpp/functions include path. Tests that need
+# real symbols (linking against fn_framework etc.) can call
+# target_link_libraries(${name} PRIVATE fn_framework imgui ...) afterwards.
+function(add_fn_test name)
+    add_executable(${name} ${ARGN})
+    target_link_libraries(${name} PRIVATE catch2)
+    target_include_directories(${name} PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/../functions
+        ${CMAKE_CURRENT_SOURCE_DIR}/../framework)
+    add_test(NAME ${name} COMMAND ${name})
+endfunction()
+
+# --- Tests reales (logica pura, no necesitan ImGui context) ----------------
+add_fn_test(test_tween_curves test_tween_curves.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/../functions/core/tween_curves.cpp)
+add_fn_test(test_pie_chart_math test_pie_chart_math.cpp)
+add_fn_test(test_kpi_card_math  test_kpi_card_math.cpp)
+add_fn_test(test_bar_chart_math test_bar_chart_math.cpp)
+
+# --- Placeholders para primitivos UI (logica visual cubierta en 0048) ------
+add_fn_test(test_tokens           test_tokens.cpp)
+add_fn_test(test_button           test_button.cpp)
+add_fn_test(test_select           test_select.cpp)
+add_fn_test(test_text_input       test_text_input.cpp)
+add_fn_test(test_badge            test_badge.cpp)
+add_fn_test(test_kpi_card         test_kpi_card.cpp)
+add_fn_test(test_pie_chart        test_pie_chart.cpp)
+add_fn_test(test_bar_chart        test_bar_chart.cpp)
+add_fn_test(test_tree_view        test_tree_view.cpp)
+add_fn_test(test_modal_dialog     test_modal_dialog.cpp)
+add_fn_test(test_toolbar          test_toolbar.cpp)
+add_fn_test(test_toast            test_toast.cpp)
+add_fn_test(test_empty_state      test_empty_state.cpp)
+add_fn_test(test_page_header      test_page_header.cpp)
+add_fn_test(test_dashboard_panel  test_dashboard_panel.cpp)
+add_fn_test(test_dashboard_grid   test_dashboard_grid.cpp)
+add_fn_test(test_sparkline        test_sparkline.cpp)
+add_fn_test(test_table_view       test_table_view.cpp)
+add_fn_test(test_icon_button      test_icon_button.cpp)