Returns the paginated list of companies the authenticated user belongs to
(for Cardda staff, all companies). This is the non-company-scoped
discovery endpoint — it does not require the company-id header, because
it is exactly how a client discovers which companies (and therefore which
company-id values) it may operate on.

Each item is augmented with the computed counters n_users, n_cards,
n_virtual_cards and owner_id. The financial balance method is added
only for Cardda staff.

Supports the standard list query parameters (_start, _end, _order,
_field) plus MongoDB-style filters passed as query params (e.g.
identifier, name, verification_status), where each value may be a plain
value or a JSON operator object such as {"$in":["..."]}.