feat(packages): ludic.shop - prices by standing with the fountain guard, a weekly demand on its own dice, stock, buying and selling through purse and pack ports, a trade fact

Items (base price, sell fraction) and vendors (stock, buys, refuses) are the game's data handed
over at boot; standing, the day, a shortage and "buys beyond its list" are the ShopWorld port;
money is ShopPurse and the pack ShopPack. The week's wanted and glutted items come from an Rng
seeded by the week, never the world's. The balance invariants - a shop is not a fountain,
friction falls and never inverts, raw keeps its order - are the package's tests (nine).

ludic.crafting: its private names carry the package's prefix too (a private name is still one
global namespace with the game's - ludic.shop's `sp_seed` met the game's).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.shop/system.ludic

@@ -0,0 +1,13 @@
+# system.ludic - the shop as a system: a reset and nothing saved (the week's demand follows from
+# the day, and nobody is at a counter across a save)
+export function shop_reset() -> void {
+  shop_at = -1
+  shop_demand_reset()
+  q_clear(shop_trades())
+}
+
+export function shop_system() -> System {
+  let s = system_new("shop", PH_COMMIT)
+  s.reset = fn shop_reset
+  return s
+}