Expose missing DataLoader-backed nested GraphQL relationships (v2)

## Objective

Fill in missing nested object/connection fields on v2 Strawberry GraphQL types that expose only a foreign-key \*_id scalar, so related entities are graph-navigable in a single query (no separate lookup / no client-side id->object mapping). Each child reuses an already-registered DataLoader or the existing search adapter; no N+1.

## Scope

Spun off from the BA-6809 audit of the GQL v2 layer. Each child is an independent, self-verifiable change with its own draft PR.

JIRA Issue: BA-6816

Start by locating the v2 Strawberry GraphQL types that expose foreign-key *_id scalars, then inspect the already-registered DataLoaders and existing search adapter. Choose one missing nested object or connection field; it is done when the related entity is queryable in one GraphQL request without client-side mapping or N+1 lookups.

Written by the indexing model from the issue text.