related must support JSON:API to-one object and null responses

[artpar]

Summary

daptin-cli related assumes JSON:API data is an array and rejects a valid
to-one relationship response object.

Reproduced with daptin-cli v0.9.0 / 56c4ba0 and Daptin v0.12.36.

Reproduction

Schema: ticket belongs_to project.

daptin-cli related ticket <ticket-reference-id> project_id

The server correctly returned JSON:API data: { ... } for the to-one relation.
CLI failed:

malformed related response: expected JSON:API data array

Expected behavior

• Accept data object for to-one, array for to-many, and null for an empty
  nullable to-one relation.
• Preserve table/JSON output and relation metadata.
• --quiet prints the one target reference id or nothing for null.
• Pagination flags should either be ignored/documented for to-one or rejected
  clearly.

Acceptance test

Cover belongs-to present/null and has-many empty/nonempty response shapes,
including --output json and --quiet.

[artpar]

daptin-cli-way rationale audit

The CLI README itself demonstrates related document <ref> user_account_id,
which is a to-one relationship. Daptin's documented relationship endpoint
returns a JSON:API object for to-one, array for to-many, and may return null.

The command currently accepts only arrays, so the documented CLI shape cannot
work for belongs-to/to-one. Keeping this as a narrow decoder bug; no new command
or server behavior is requested.