mv2: Support nearly every type of message deletion

[FlaminSarge]

• Delete self messages, on own or other streams (retract a message)
• Streamer/mods can delete others' messages
• Removed messages get italic/faded style (as before). Pending removals get a strikethrough. The entire line gets 50% opacity, so emoji-only message deletions can be detected by the avatar/username getting faded.
• Removal success alert no longer shows, instead doing the style changes above.
• Moderators will see "View deleted message" to show the original message
• Already-deleted messages no longer show the delete option
• If someone else deletes their own message it'll show the strikethrough/etc.
• Adjust the style of the dropdown menu buttons

Fair warning: Claude-assisted.