The round timer relied on each client's own wall clock, so two browsers with
skewed local clocks showed different countdowns for the same round; the
server now also returns server_time so the frontend can correct for clock
skew. Also drop out-of-order /rounds/current responses (multiple independent
triggers could resolve late and revert the UI to a stale drawing/result
state) and prune per-round bookkeeping maps on round transitions.
Separately, place_bet only checked status == "open", leaving a window (up to
the scheduler's 5s tick interval) after a round's timer hit zero where a new
bet could still be accepted. place_bet now checks the round's own deadline
directly (round_accepts_bets), acting as an immediate "yellow light" for new
entries while still letting already-broadcast bets confirm before the round
closes.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>