feat(currency): money moves through the bounded vocabulary (§6)

give_item(gold) is +10,000c and does NOT mark gifts_given — that gate is a
global one-shot keyed by item id, so marking money would let an NPC pay you
exactly once per campaign. accept_item(<denom>) is offered only for the
denominations the purse can actually pay.

The eight moves do not grow. MoveValidator is untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QYa9u7Kdxv5gX4AnwWexy8

client/scripts/npc/npc_content.gd

@@ -21,12 +21,20 @@ static func available_moves(npc_dict: Dictionary, game_state, canon_log) -> Arra
 			moves.append("reveal(%s)" % t)
 
 	for i in caps.get("giveable_items", []):
-		if not game_state.is_gift_given(i):
+		# Currency is exempt from the one-shot gift gate — an NPC can pay you twice.
+		if Currency.is_currency(i) or not game_state.is_gift_given(i):
 			moves.append("give_item(%s)" % i)
 
 	for item_id in game_state.inventory.keys():
 		if int(game_state.inventory[item_id]) > 0:
 			moves.append("accept_item(%s)" % item_id)
 
+	# Money is not in the inventory dict, so it needs its own offer. Only the
+	# denominations the purse can actually pay: an NPC cannot ask a party holding
+	# 47c for a gold coin.
+	for denom in Currency.VALUES:
+		if game_state.purse_copper >= Currency.value(denom):
+			moves.append("accept_item(%s)" % denom)
+
 	moves.append_array(UNIVERSAL)
 	return moves