AR frontend: Repository list + plumbing

Part of epic Repository read (+ plumbing), slice 1.

Repository list view + the shared frontend plumbing (Ruby REST client, credential-provider interface + stub, error mapping, Apollo client, routing shell, feature flag), plus filtering, sort, and cursor pagination.

Scope

• GraphQL Repository type (list fields): format, name, type, visibility, downloads, size, lastUpdatedAt; aggregate count + total size
• repositories(filter, sort, pagination) resolver → AR list endpoint (1:1 client mapping)
• Credential-provider stub (dev/bootstrap), behind the interface the real exchange will implement
• Error mapping: auth → not-available, transport → service-unavailable
• Filtering (is / is not), format facet, sort, cursor pagination
• No cross-service joins (the list shows none)

Design

• Repository list
• Filtering / sort / search

Depends on

• AR REST list endpoint + per-element payload + cursor pagination shape: artifact-registry S17 / ADR-009