Allow users to hide annotations from their own view

[mkdir-washington-edu]

Slack conversation: https://hypothes-is.slack.com/archives/C2C2U40LW/p1733142323654149

The problem:
Users may get Spam (and other) replies and want to hide those replies from their view. Unless they're the moderator of the group they're annotating in, they cannot do so.

A solution:
When users mark a comment as Spam, hide the annotation from their view immediately (while still following the normal workflow for flagged annotations). Because some users mistakenly use the flag button for non-moderation reasons (thinking it's a bookmark or a "+1" button) we may wish to add a step where they can un-hide these hidden annotations.

Related issues:

• Issue that spawned the Slack thread: let me remove spam comments from my annotations h#9163
• Be able to hide annotations without flagging them first #829