Wires the frontend half of the read-only RFC. The Settings → GitHub tab
now always issues the installation list query for any workspace member
(the backend gates it via `RequireWorkspaceMember` after PR #2886) and
gets `can_manage` straight from the API response. The render matrix
covers the six cases the RFC calls out:
- configured + connected + admin → Disconnect + (optional) Connected by
- configured + connected + member → read-only "Connected to" + read_only_hint
- configured + not connected + admin → Connect button + dev description
- configured + not connected + member → contact_admin_to_connect hint
- not configured + admin → operator banner + disabled Connect
- not configured + member → contact_admin_to_connect hint
New i18n keys (en + zh-Hans): read_only_hint, connected_by, contact_admin_to_connect.
The unused github.manage_hint string is removed (its non-admin branch
now resolves to one of the two new hints depending on connection state).
GitHubInstallation gains an optional `connected_by` display name so the
UI can render the "Connected by {name}" line without further changes
once the backend exposes the field.
Co-authored-by: Lambda <lambda@multica.ai>
Co-authored-by: multica-agent <github@multica.ai>
