Message composer & feed parity gaps #17

Summary

:feature:messages covers posting, replies, digs, delete, search, media upload, scheduling
(create + cancel), reporting, link-preview metadata, edit and author moderation. Several
first-class web behaviours are still missing, and two of them (visibility and feed view
preferences) change what a post is and who sees it — so they rank P0.

Verified gaps

CreateMessageRequest in feature/messages/.../dto/MessagesResponse.kt sends
content, parentId, imageUrls, videoUrls, scheduledAt, mastodonProviderIds, crossPostTo{Bluesky, LinkedIn,Twitter}.

POST /api/messages also accepts — and the app never sends — publiclyVisible, tags[],
pushedMessageId, organizationId, linkedInTargets[] and
linkedInLinkAsFirstComment.

GET /api/messages accepts onlyMine, tag and an opaque cursor for keyset pagination;
MessagesApi.getMessages still sends limit/offset only.

Done when

Every sub-issue is closed and a post made from Android can carry the same properties as one made
on the web.

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