end_vote_round does not clean up trustauth's round state #32

Ending a vote round resets the server's VoteAuthority and unlocks the meeting, but never informs trustauth. The old RoundState (including the BLS keypair) stays in trustauth's rounds map until it is overwritten by the next start_vote. After multiple rounds without subsequent starts, stale entries accumulate in trustauth memory indefinitely.

File: rustsystem-server/src/api/host/end_vote_round.rs

Fix: Call a trustauth end-round endpoint (to be created) from end_vote_round, or have trustauth clean up on start-round for the same muuid.