Combat: per-round !cast / !consume in turn-based fights

Turn-based Elite/Boss fights gain !cast and !consume as player-turn
actions, so casters and item-users make decisions per round instead of
pre-queuing a single effect. The command handler validates and resolves
the spell/item into a pre-rolled turnActionEffect; the engine just
applies the HP deltas and flows on into the enemy turn.

Scoped to effects that resolve within the casting round: damage, heal,
and control spells, plus heal/flat-damage consumables. Buff and utility
spells and buff-type consumables are refused without spending the
resource — they need cross-round stat persistence, a later sub-phase.

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

internal/plugin/adventure.go

@@ -330,6 +330,9 @@ func (p *AdventurePlugin) OnMessage(ctx MessageContext) error {
 	if p.IsCommand(ctx.Body, "flee") {
 		return p.handleFleeCmd(ctx)
 	}
+	if p.IsCommand(ctx.Body, "consume") {
+		return p.handleConsumeCmd(ctx, p.GetArgs(ctx.Body, "consume"))
+	}
 	if p.IsCommand(ctx.Body, "expedition") {
 		return p.handleDnDExpeditionCmd(ctx, p.GetArgs(ctx.Body, "expedition"))
 	}