Highlight unread messages in room view

[sgrimee]

Summary

Add visual highlighting for unread messages in the room view to help users quickly identify new content.

Requirements

• Visually distinguish unread messages from read messages in the room view
• Track read/unread status for messages
• Update read status when messages are viewed
• Clear visual indication of what constitutes "unread"

Implementation Notes

• This should use appropriate styling that will be compatible with future configurable theming
• Consider different highlight methods: background color, border, text style, or indicator symbols
• Maintain performance with large message lists
• Integrate with existing message display logic

Acceptance Criteria

• Unread messages are visually distinct in the room view
• Read status updates appropriately when messages are viewed
• Highlighting works consistently across different message types
• Performance remains acceptable with large message histories

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