Account: surface account status, posting restrictions and the appeal path #73

Part of #71 — Account lifecycle & security completeness

/help/account documents Account status, why posting is limited on a new account, and
appealing a restriction or suspension. Android shows none of this — a restricted user just
sees posts fail.

• Read the account status from the user payload and show it in the Account hub.
• When posting is limited, explain why at the point of failure rather than surfacing a raw
  error.
• Link the appeal path.

Tests: restricted-account state renders; composer shows the explanation instead of a generic
error.

Filed from the parity review of feature/parity-wip @ 14d7795 against interlinedlist.com (OpenAPI /api/openapi.json, 233 paths) and the public help centre.