refactor(ui): shared searchable CustomerPicker across offers/invoices/issued-orders

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/ui/index.ts

@@ -9,6 +9,7 @@ export type { DataColumn } from "./DataTable";
 export { Field, SwitchField } from "./Field";
 export { default as Select } from "./Select";
 export type { SelectOption } from "./Select";
+export { default as CustomerPicker } from "./CustomerPicker";
 export { default as StatusChip } from "./StatusChip";
 export { CheckboxField } from "./Checkbox";
 export { default as Alert } from "./Alert";