Combat: wire turn-based elite/boss fights to the command surface

Routes Elite/Boss rooms off the auto-resolve SimulateCombat path and onto
the persisted turn-based engine. !zone advance now stops at an Elite/Boss
doorway; the player engages with !fight, then resolves one full round per
!attack / !flee. A won CombatSession is the record that the room's combat
is done, so a fresh !zone advance clears the room and advances the graph.

- buildZoneCombatants: shared player/enemy Combatant builder extracted from
  runZoneCombat; combatantsForSession rebuilds the pair from a session row.
- runCombatRound loops the phase state machine through a whole round;
  finishCombatSession runs HP/XP/loot/kill/threat/mood close-out.
- getCombatSessionForEncounter lets the room resolver tell "already won"
  apart from "not yet fought".
- !zone advance/enter/go blocked while a session is active.
- resolveBossRoom deleted (dead after the reroute).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/adventure.go

@@ -321,6 +321,15 @@ func (p *AdventurePlugin) OnMessage(ctx MessageContext) error {
 	if p.IsCommand(ctx.Body, "zone") {
 		return p.handleDnDZoneCmd(ctx, p.GetArgs(ctx.Body, "zone"))
 	}
+	if p.IsCommand(ctx.Body, "fight") {
+		return p.handleFightCmd(ctx)
+	}
+	if p.IsCommand(ctx.Body, "attack") {
+		return p.handleAttackCmd(ctx)
+	}
+	if p.IsCommand(ctx.Body, "flee") {
+		return p.handleFleeCmd(ctx)
+	}
 	if p.IsCommand(ctx.Body, "expedition") {
 		return p.handleDnDExpeditionCmd(ctx, p.GetArgs(ctx.Body, "expedition"))
 	}