Demote one organisation's HTTP API style from MUST to an example #2130

Part of #2124.

backend/http.md states one house style as universal MUST. A project with its own API guide must break these rules to keep it.

• :37-45 paths: lowercase hyphens, American English, no abbreviations
• :48-52 camelCase query names; reserved limit, skip, offset, expand, sortedBy
• :96-109 a links array with href, rel, type and media; backend/api.md:90 depends on it

Done when

• Protocol-level rules stay: methods, status codes, RFC 9457 errors, timeouts
• The style rules become an example the project adopts, or SHOULD with a reason