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/backend/src/routes/v1/transactions.ts

@@ -27,6 +27,8 @@ export const transactionRoutes: FastifyPluginAsync = async (app) => {
       status: query.status,
       transactionType: query.transactionType,
       locationId: query.locationId,
+      accountId: query.accountId,
+      itemSearch: query.itemSearch,
     }
 
     const result = await TransactionService.list(app.db, params, filters)