feat: customer lookup from POS with order history and item search

- Customer dialog in cart panel: search accounts by name, phone, email, account #
- Selected customer shown with name, phone, email in cart header
- accountId passed when creating transactions
- Order history view: tap a transaction to expand and see line items
- Item search in history (e.g. "strings") — filters orders containing that item
- Backend: add accountId and itemSearch filters to transaction list endpoint
- itemSearch uses EXISTS subquery on line item descriptions (ILIKE)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/admin/src/api/pos.ts

@@ -151,7 +151,7 @@ export function discountListOptions() {
 // --- Mutations ---
 
 export const posMutations = {
-  createTransaction: (data: { transactionType: string; locationId?: string }) =>
+  createTransaction: (data: { transactionType: string; locationId?: string; accountId?: string }) =>
     api.post<Transaction>('/v1/transactions', data),
 
   addLineItem: (txnId: string, data: { productId?: string; inventoryUnitId?: string; description: string; qty: number; unitPrice: number }) =>