fix(mcp): expose price fields on all create tools so AI can link costs to items

Add price/currency params to create_place, create_and_assign_place,
create_place_accommodation (passed through to createPlace which already
persists them). Add price/budget_category to create_transport and
create_reservation: price is written to metadata.price (shown on the
booking) and a linked budget_items row is created via a new
linkBudgetItemToReservation helper in budgetService (also used to
de-duplicate the existing route-level logic in routes/reservations.ts).

Fixes #1031

server/src/services/budgetService.ts

@@ -96,6 +96,17 @@ export function createBudgetItem(
   return item;
 }
 
+export function linkBudgetItemToReservation(
+  tripId: string | number,
+  reservationId: number,
+  data: { name: string; category?: string; total_price: number },
+) {
+  const item = createBudgetItem(tripId, data) as BudgetItem & { reservation_id?: number | null };
+  db.prepare('UPDATE budget_items SET reservation_id = ? WHERE id = ?').run(reservationId, item.id);
+  item.reservation_id = reservationId;
+  return item;
+}
+
 export function updateBudgetItem(
   id: string | number,
   tripId: string | number,