feat(view): D4 Design View action family + reapply-on-open wiring

Register toggle/activate/tag/untag/show-both actions driving the D2
shell and D3 model; reapply saved active mode on project load via a
persist load-signal seam. Shared guidString helper; pure nextModeId
unit-tested.

CMakeLists.txt

@@ -116,6 +116,8 @@ add_library(reaper_reasampler MODULE
     src/view_mode_model.cpp
     src/view_tree.cpp
     src/view.cpp
+    src/track_guid.cpp
+    src/actions.cpp
 )
 target_link_libraries(reaper_reasampler PRIVATE bank_model capture_paths peaks bank_grid view_mode_model)
 target_include_directories(reaper_reasampler PRIVATE ${SDK_INC} ${WDL_INC})