fix(plan-lifecycle): correct DoD gating test assertions

The test scenario 'validation_summary is populated after DoD evaluation'
was expecting 'total' and 'required_passed' keys which are not added by
the DoD evaluation. These keys are only present when the plan goes through
the Execute phase validation gate. The DoD evaluation only adds
'dod_evaluated', 'dod_all_passed', and 'dod' keys.

Updated the test to check for the 'dod' key instead, which correctly
reflects the structure of the validation_summary after DoD evaluation.

ISSUES CLOSED: #7927

features/plan_dod_gating.feature

@@ -65,8 +65,7 @@ Feature: Definition-of-Done Gating in Apply Phase
     When I apply the plan with DoD gating
     Then the plan validation summary should contain key "dod_evaluated" with value true
     And the plan validation summary should contain key "dod_all_passed" with value true
-    And the plan validation summary should contain key "total"
-    And the plan validation summary should contain key "required_passed"
+    And the plan validation summary should contain key "dod"
 
   # --- DoD gating integrates with full lifecycle ---