research(federation): evaluate Bonfire Networks as federation substrate

[Argocyte]

Evaluate Bonfire Social + Community (NOT Cooperation/Coordination per A10) as the ActivityPub federation surface. Assess Circles/Boundaries as inter-coop @mentions primitive. Assess GraphQL API integration path (no Elixir development). Warm lead at bonfire-networks/bonfire-app#1938. Ref: R2 reference_bonfire_networks.md. UUID: 4ee7e456-7944-450e-94c0-af1ae8eac1f4. Filed by Et under G5/A7.