FL-1503: reply and community display fields in PostCommentCreated

Replies to comments (FL-1425). Optional fields in cms.PostCommentCreated, all additive — consumers on v1.67.0 keep working.

Reply fields (absent for a top-level comment)

• parentId — top-level comment of the thread (one level of nesting, never a reply)
• replyToCreatorId — real author of the comment actually answered (the "replied" push recipient). Not the top-level author: A → B → C gives parentId = A's comment, replyToCreatorId = B. Absent when the author is deleted.
• replyToPostedAsCommunity — the answered comment is a community comment → NMS pushes the community's managers
• IsReply(); Validate rejects reply fields without parentId and zero uuids

Community display — a push about a comment posted as the community must never show the person who wrote it

• postedAsCommunity
• community: {name, logo} (*CommunityDisplay, review): name required, logo a full CDN URL or absent; only together with postedAsCommunity
• flag without community = community deleted → no author shown
• communityId / communityManagerIds stay flat (FL-1405 contract, already in main)

Tags pushed for the stand: v1.68.0-rc.1 … v1.68.0-rc.4 (rc.4 = this branch head). After merge → v1.68.0, then CMS (FL-1503) and NMS (FL-1504) bump to it.

Contract: https://freedomgroupinternational.atlassian.net/wiki/spaces/fig/pages/374112259

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