feat(tests): reopen rejected test keeps all content + rejection notes

Backend (reopen_test):
- Preserve red/blue validation NOTES — teams see exactly what to fix
  without losing the rejection context. Previously both notes were cleared.
- Preserve all content fields: procedure_text, tool_used, red_summary,
  attack_success, blue_summary, detection_result (already the case).
- Preserve evidences (separate table, unaffected — already the case).
- Still clear: validation statuses + who/when validated (fresh re-validation
  required). Phase timing reset so the new execution starts clean.

Frontend:
- Button label: 'Reopen Test' → 'Continue Test' (more accurate intent)
- Dialog title: 'Reopen Test' → 'Continue Test'
- Dialog message: replaces alarming 'workflow will be restarted / clear all'
  with accurate description of what is preserved vs reset
- Toast: explains what to do next

backend/app/services/test_workflow_service.py

@@ -655,27 +655,33 @@ def get_retest_chain(db: Session, test_id) -> list[Test]:
 
 
 def reopen_test(db: Session, test: Test, user: User) -> Test:
-    """Move a ``rejected`` test back to ``draft``, clearing validation fields.
+    """Move a ``rejected`` test back to ``draft`` for continued work.
 
-    This allows the teams to redo the test cycle.
+    Preserves all content (procedure, summaries, evidences) and — crucially —
+    the rejection NOTES so teams know what to fix without losing context.
+
+    Clears validation decisions (status, who validated, when) so leads must
+    re-validate the updated submission.  Phase timing is reset so the timer
+    starts fresh for the new execution attempt.
     """
     test = transition_state(
         db, test, TestState.draft, user,
         action_name="reopen_test",
     )
 
-    # Clear dual-validation fields
+    # Clear validation DECISIONS — leads must re-validate the new attempt.
+    # Rejection NOTES are intentionally kept so teams see what needs fixing.
     test.red_validation_status = None
     test.red_validated_by = None
     test.red_validated_at = None
-    test.red_validation_notes = None
+    # test.red_validation_notes → KEEP (rejection reason / clarification needed)
 
     test.blue_validation_status = None
     test.blue_validated_by = None
     test.blue_validated_at = None
-    test.blue_validation_notes = None
+    # test.blue_validation_notes → KEEP (rejection reason / clarification needed)
 
-    # Clear phase timing fields
+    # Reset phase timing so the new execution starts fresh
     test.red_started_at = None
     test.blue_started_at = None
     test.blue_work_started_at = None