Add D5 Design-View mode switch to bank panel

New pure mode_switch module (header-rect -> N equal segment rects + point hit-test, unit-tested) plus a segmented switch in the bank_panel header: one lit segment per registered mode, click activates via view::applyMode. Grid offset below the header.

CMakeLists.txt

@@ -45,6 +45,16 @@ target_include_directories(capture_paths PUBLIC src)
 add_library(bank_grid STATIC src/bank_grid.cpp)
 target_include_directories(bank_grid PUBLIC src)
 
+# ---------------------------------------------------------------------------
+# 2c') Pure mode_switch layout — NO REAPER, NO SWELL. The Design-View mode-switch
+#      geometry (D5): header rect + N modes -> N equal segment rects (exact tiling),
+#      and point -> segment hit-test. Split out so the switch's layout math is
+#      unit-tested outside the DAW; the bank_panel header strip that draws it and
+#      routes clicks to view::applyMode is DAW-verified. Mirror of bank_grid.
+# ---------------------------------------------------------------------------
+add_library(mode_switch STATIC src/mode_switch.cpp)
+target_include_directories(mode_switch PUBLIC src)
+
 # ---------------------------------------------------------------------------
 # 2d) Pure view_mode_model library — NO REAPER, NO SWELL. The Design View heart
 #     (Phase D1): mode registry + GUID-keyed membership index + folder-tree-aware
@@ -106,6 +116,10 @@ add_executable(bank_grid_tests tests/test_bank_grid.cpp)
 target_link_libraries(bank_grid_tests PRIVATE bank_grid)
 add_test(NAME bank_grid_tests COMMAND bank_grid_tests)
 
+add_executable(mode_switch_tests tests/test_mode_switch.cpp)
+target_link_libraries(mode_switch_tests PRIVATE mode_switch)
+add_test(NAME mode_switch_tests COMMAND mode_switch_tests)
+
 add_executable(view_mode_model_tests tests/test_view_mode_model.cpp)
 target_link_libraries(view_mode_model_tests PRIVATE view_mode_model)
 add_test(NAME view_mode_model_tests COMMAND view_mode_model_tests)
@@ -141,6 +155,7 @@ add_library(reaper_reasampler MODULE
     src/capture.cpp
     src/persist.cpp
     src/bank_panel.cpp
+    src/mode_switch.cpp
     src/insert.cpp
     src/insert_plan.cpp
     ${LICE_SRC}
@@ -151,7 +166,7 @@ add_library(reaper_reasampler MODULE
     src/actions.cpp
     src/render_settings.cpp
 )
-target_link_libraries(reaper_reasampler PRIVATE bank_model capture_paths peaks bank_grid view_mode_model insert_plan render_settings)
+target_link_libraries(reaper_reasampler PRIVATE bank_model capture_paths peaks bank_grid mode_switch view_mode_model insert_plan render_settings)
 target_include_directories(reaper_reasampler PRIVATE ${SDK_INC} ${WDL_INC})
 set_target_properties(reaper_reasampler PROPERTIES PREFIX "" OUTPUT_NAME "reaper_reasampler")