List LinkedIn sender accounts for the org (resolver helper)

Return LinkedIn sender accounts for sender_account_id resolution.

Resolves the sender_account_id on the Netrion workflow nodes (send_netrion_connection_request / send_netrion_message) and on the linkedin_* triggers' linkedin_account_id. Until this existed there was NO way to discover these ids programmatically: voice's _RESOLVER_HINTS said "no MCP resolver yet — ask user", and the only listing endpoint (GET /v1/linkedin/accounts) is behind get_current_user browser auth, so an MCP/API caller could build the node and then not attach a sender.

sender_account_id is the INTEGER PK (ArlinkLinkedInAccount.id), which is the value the node config takes — deliberately NOT the arlink lia_... string. account_resolution.resolve_active_account cannot parse the lia_ form, and the Netrion nodes opt into strict_account, so naming one is a hard failure rather than a silent send from an arbitrary seat. The field is emitted as a STRING because that is the node config's own type.

Mirrors GET /v1/linkedin/accounts on degradation: flag off, no accounts, or per-org tables not provisioned all answer an empty list, never a 500. A sender that is not status='OK' is still returned, with its status, so the caller can say "that seat is disconnected" instead of "no seats".