Entity gains location from Object and narrows x/y back to int
(entities always have spatial coordinates). No behavioral change —
all existing tests pass unchanged.
Phase 1 of fightable mobs: MobTemplate dataclass loaded from TOML,
global mobs list, spawn_mob/despawn_mob/get_nearby_mob with
wrapping-aware distance. Mob entity gets moves and next_action_at fields.
Defenses now work outside combat mode with stamina cost, recovery lock
(based on timing_window_ms), and broadcast to nearby players. Lock
prevents spamming defenses — you commit to the move. Stamina deduction
moved from encounter.defend() to do_defend command layer. Defense
commands registered with mode="*" instead of "combat".
