feat(api): filter entities by current owner

Why

The redesigned entity detail page uses entity.kind for its presentation. Company records need to show their owned distilleries, brands, bottlers, and other companies. The current entity details response exposes only ownerId, and entities.list cannot filter by owner. The web page must not infer a company portfolio from bottle relationships.

API contract

• Add an optional numeric owner filter to GET /entities.
• Filter on the entity current-owner relationship (ownerId).
• Preserve the existing cursor, limit, type, sort, and location behavior.
• Support the same filter in the typed mock API.
• Return the existing entity-list envelope and serialized entity records; no new response shape is needed.

Web use

The company entity detail page will request owned entities, group the supplied records by kind, and link to their detail pages. Until this capability exists, the redesign will show the company identity and owned core facts but will not invent a portfolio section from the entity catalog.

Acceptance criteria

• entities.list({ owner: companyId }) returns only entities whose current ownerId matches the company.
• The filter composes with type, sort, and cursor inputs.
• Unknown or empty portfolios return the standard empty list response.
• The mock API includes a company with owned entities so the web page can be reviewed locally.

Start at the GET /entities implementation and the entities.list typed mock API entry point. Add the optional owner filter while preserving type, sort, cursor, limit, location, and the existing response envelope; verify matching, empty, and composed-filter behavior, including a mock company with owned entities.