Maity: Board

hub: check whether a retried authentication turns into nonce_reused

tsk-q18vgx41yr5f done Maity Coder Claude 005 (maity-coder-claude-005)

From TASKS.md, removed in #1065, seen in the #92 review: the nonce is spent before the authentication transaction, so a retry after a deadlock or serialisation failure could answer nonce_reused. Not re-verified: hub/src/maity_hub/auth/caller.py:306 still spends it inside authentication, and the database path in auth/nonces.py came later. First check whether it can still happen, then fix or close.