Commenting support

Describe the feature

Features:

• comment threads, allowing someone to reply to a specific comment
• mention a field in the entry (nice to have)
• reference another entry which is rendered as a link in the comment (nice to have)
• comment authors
• comment only permission
• resolving comments
• comment reactions?
• comment activity, per device CommentId tracks read status, local only.
• Permissions, edit delete your own, managers can delete any comment or thread. Comment only has the same permissions as editor.
• Limit text to 2k chars, reject empty comments.
• import LF comments (nice to have)

UI:

• On each entry/sense/example comments can be made and seen as threads which have to be explicitly opened, this is to help handle read status.
• There should be a sort of activity view to find unread comments or threads. By default it should sort by comment date and filter to only unread comments. There should be a button to mark all as read. It would be nice to have a toggle to change the sort order by sync date, and show all comments. MVP UI can just list comments, we can expand it to list per thread or per subject later. There should be a way to jump to the entry/subject that the comment was made on.
• If a comment was edited (eg CreateDate != UpdatedDate) then highlight that in the UI.
• Show a comment history button if edited.

No files, tests, or entry points are named. Before implementation, split the requested comment, permission, activity, and UI behaviors into an agreed MVP with acceptance criteria; done should be defined before work starts.