Resolve External Ids

Resolve raw channel-side external IDs to human-readable contact names.

Used by the agent-trigger "Restrict to specific senders" UI to render chips with the contact's display name instead of raw numeric IDs. entity.channel_ref stores the channel-prefixed form (<channel>:<external_id>) so we match on the suffix.

Returns one entry per supplied id. If a row can't be resolved (no entity match in the workspace), the id is echoed back with channel=null and title=null — the UI falls back to displaying the raw id, which is still better than failing the page.

Workspace-scoped via the entity.workspace_id predicate (get_workspace_session already routes the DB connection, but we add the explicit filter as defense-in-depth — entity rows are not partitioned).