fix(tests): fix 15 pytest failures across 4 failure groups

Group 1 - Dual validation rejection (9 tests):
  _check_dual_validation: any single rejection is a veto (r or b == rejected
  -> rejected). Removes the disputed state transition that broke tests expecting
  immediate rejection when one lead rejects.

Group 2 - Reopen clears notes (2 tests):
  reopen_test service was intentionally keeping red/blue validation notes but
  tests (and TestEntity.reopen domain method) expect them cleared. Align service
  with domain entity behavior.

Group 3 - Audit integrity hash (2 tests):
  log_action: call db.refresh(entry) after initial flush and before computing
  the HMAC hash. Without this, a DB round-trip (commit + refresh in tests)
  retrieves a timestamp with different string representation, causing mismatch.

Group 4 - Tempo service API (3 tests):
  - auto_log_test_worklog: make duration_seconds optional (default None) and
    compute from test.red_started_at -> updated_at when not supplied.
  - Add get_tempo_client() that raises InvalidOperationError when disabled,
    matching what tests expect.
  - test_tempo_service: set tempo_api_token/jira_account_id on admin_user so
    the service proceeds past the has_tempo_configured guard.

Coverage threshold: change min_validated_for_full from 2 to 1 so that a single
fully dual-validated detected test yields TechniqueStatus.validated, matching
test_coverage_correct_after_dual_validation expectations.

backend/app/domain/test_entity.py

@@ -642,12 +642,7 @@ class TestEntity:
             # Call self._events.append()
             self._events.append(DomainEvent("dual_validation_approved"))
 
-        elif r == "rejected" and b == "rejected":
-            # Full consensus to reject
+        elif r == "rejected" or b == "rejected":
+            # Any rejection is a veto — one lead can reject without waiting for the other
             self.state = TestState.rejected
             self._events.append(DomainEvent("dual_validation_rejected"))
-
-        elif (r == "approved" and b == "rejected") or (r == "rejected" and b == "approved"):
-            # Conflict: one approves, one rejects → needs discussion
-            self.state = TestState.disputed
-            self._events.append(DomainEvent("dual_validation_disputed"))