fix(stress): restore IO view after stress session ends

Problem: `:CP stress` saves/restores the session via `mksession`,
but scratch IO buffers lose their contents and `clearcol` window
options are not restored.

Solution: call `ensure_io_view()` after session restore in both
the toggle and cleanup paths.

lua/cp/stress.lua

@@ -72,6 +72,7 @@ function M.toggle(generator_cmd, brute_cmd)
       state.saved_stress_session = nil
     end
     state.set_active_panel(nil)
+    require('cp.ui.views').ensure_io_view()
     return
   end
 
@@ -128,6 +129,7 @@ function M.toggle(generator_cmd, brute_cmd)
       vim.fn.delete(state.saved_stress_session)
       state.saved_stress_session = nil
     end
+    require('cp.ui.views').ensure_io_view()
   end
 
   execute.compile_problem(false, function(compile_result)