Add KDoc to the single-interface feature API modules
Cover the last remaining interfaces across features/announcement, cachecleaner,
call, contentscanner, createroom, knockrequests, lockscreen, rolesandpermissions,
startchat, userprofile and viewfolder, with their members and parameters.
Grouped into one commit rather than eleven near-empty ones, per the AGENTS.md rule
about tiny commits.
This completes every features/* api module.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
