Replace mocked admin flows with live backend data and error states

[juliuskrah]

Parent initiative: #287

Summary

Replace mocked admin workflows with live backend data so the commerce admin reflects real GitStore resources and operator console failure states.

Acceptance criteria

• Enabled admin views use committed GraphQL queries and mutations instead of static fixtures for primary workflows.
• Mock-only flows are removed, feature-gated, or marked unavailable until the backing API capability exists.
• Loading, empty, unauthorized, validation, conflict, network, and server error states are mapped consistently.
• Catalog operations, context switching, search, and detail pages refresh after successful mutations.
• Tests cover live data adapters, fixture removal, error mapping, and regression paths for previously mocked flows.

Architecture note

gitstore-admin remains an optional add-on and consumes gitstore-api; it must not talk directly to gitstore-git-service.