Navigate from group chat notifications to group room

[barrydeen]

Summary

• Group chat notifications (reactions, zaps) now expand to show the actual message content with custom emoji support and a group name badge, instead of an infinite-spinner PostCard
• Clicking the expanded message navigates to the group room and scrolls to + highlights the specific message
• Highlight animation clears after 1.5s instead of blinking indefinitely

Test plan

• Receive a reaction on a group chat message, verify it appears in notifications
• Expand the notification — verify the message content renders with custom emojis and the group name badge
• Click the expanded message — verify it navigates to the group room and scrolls to the correct message with a brief highlight
• Verify the highlight fades out and does not continue blinking