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/services/audit_service.py

@@ -110,6 +110,10 @@ def log_action(
     db.add(entry)
     # Flush changes to DB without committing the transaction
     db.flush()
+    # Reload from DB so the timestamp is in DB-stable format before hashing.
+    # Without this, a round-trip through the DB (e.g. refresh after commit) can
+    # return a timestamp with different precision/timezone, causing hash mismatch.
+    db.refresh(entry)
     # Assign entry.integrity_hash = compute_integrity_hash(entry)
     entry.integrity_hash = compute_integrity_hash(entry)
     # Return entry