Retrieve a paginated list of customers with optional filters.

Filtering options:

• number — filter by customer number(s) — exact match, repeatable: ?number=C001&number=C002
• search — general search term matching name or number (alphanumeric)

Pagination:

• pageNumber — 1-based page number (default: 1)
• pageSize — number of results per page, max 100 (default: 10)