AR manifests referrer-inclusion argument (monolith/S14 step 10)

What

Adds the includeReferrers boolean argument on the manifests connection for monolith/S14, Step 10.

• Maps to the AR contract's include_referrers, defaults to false with replace_null_with_default, keeping the schema faithful to the endpoint when the caller omits it.
• The resolver forwards the value to the Step 3 client method (which always sends include_referrers).

The design shows referrers on, so the view overrides this default to true. That is a later step, not this one. This step keeps the schema default faithful to the endpoint.

Testing

Resolver spec asserts the argument's type and false default. A request-spec case forwards includeReferrers: true to include_referrers=true over the wire; the rest of the manifests request suite pins the default false. All green locally (30 examples across the resolver and request specs); RuboCop clean; GraphQL schema and docs regenerated and in sync.

Dependencies (branch stacking)

Stacked on Step 9 (manifests sort argument, !251089 (merged)), which transitively carries Step 7 and its deps. The plan notes Steps 9 and 10 are unsequenced and both append to the same resolver, so stacking 10 on 9 keeps them a clean linear series. Review and merge order: Step 7, then 9, then 10. Until Step 9 merges, this MR's diff includes Step 9's commit.

References

• Plan: monolith/S14 plan, Step 10
• Spec: S14 connections

Feature flag artifact_registry_ui is dark. No changelog (dark); argument text is schema text, not i18n.

Related to #618410 (closed)