Various (simple) polish feature requests for Root CMS Tasks

[jeremydw]

A few features are needed to improve the feature parity with other issue tracking tools.

1. Autocomplete for "@" mentions in the comment field (can pull from other participants in the task, and also from the CMS ACL).
2. Autocomplete for "assignee" field (same source as above).
3. Addition of a new "CC list" field; which provides the ability to CC other users on issues.
4. Ability to add attachments within the comment box (e.g. paste image, it can show as an attachment nested within the comment).
5. Tooltips for all over the users on the task page. Currently users shows as just "jeremydw" but we should have the fuller tooltip visible when you hover over it (same as in the doc status badges on the doc editor page). The tooltip should show the thumbnail and name (if available), otherwise just the full email address. Right now, since just the name of the email is included (and not the domain), we don't have a way of knowing which domain the user belongs to.
6. Ability to press Cmd+Enter to send the comment.
7. Deeplinks for comment – I should be able to right click the timestamp on the comment and press "Copy link", e.g. /cms/tasks/7#comment1 and that links directly to comment 1.
8. Ability to delete/archive the issue (looks like you can only delete comments now).
9. URLs pasted into the rich text field should be automatically linkified.

[jeremydw]

One more (more significant): Preview links shared inside comments (e.g. to /foo/bar/?preview=true) are treated as SPA navigation inside Root CMS UI, which causes a 404. Thinking the SPA navigation should only handle links prefixed with /cms and all other links should be opened in a new window (with external link icon appended to them).

[jeremydw]

FYI; I've started an AI task to tackle these (with the exception of the autocomplete feature -- we can let that one be handled separately as it might be something that we want to be more reusable)

[stevenle]

fyi just spawned a task for (2) and (3)

[jeremydw]

One more feature request – the action log should have action buttons to open the task in the CMS, right now it just shows the task ID.