Attacker can change their move mid-telegraph or mid-window without
resetting the timer. Old move's stamina is refunded, new move charged.
Defender gets a fresh telegraph on switch. Feedback says "switch to"
instead of "use" when swapping attacks.
resolve() returns ResolveResult dataclass with attacker_msg, defender_msg,
damage, countered, and combat_ended fields. process_combat is now async
and sends messages to both participants on resolve. Counter, hit, and
slam messages give each player their own perspective on what happened.
