Add Real-Time Collaborative Presence in Chat

[Techhackontime999]

Description

Enhance the real-time chat with collaborative presence features: multi-device sync indicators, read-by timestamps, and online presence for chat partners.

Requirements

• Show "Active now" indicator in chat header (real-time via WebSocket)
• Read-by timestamps: show "Seen at [time]" on the last read message
• Multi-device: show when user is active on multiple devices
• Chat partner's last seen time when offline
• Typing indicator improvements: show avatar, auto-dismiss after 10s
• Message delivery confirmations: checkmark (sent), double-checkmark (delivered), blue (read)
• Presence websocket: dedicated consumer for presence updates

Files to Modify

• linkup/messaging/consumers.py - Add presence broadcast to ChatConsumer
• linkup/messaging/presence_manager.py - Enhance with multi-device tracking
• linkup/messaging/models.py - Add last_read_at to Message model
• linkup/messaging/views.py - Add read-by timestamp API
• linkup/static/js/chat.js - Update UI for presence indicators and read receipts
• linkup/templates/messaging/chat.html - Add presence UI elements

Acceptance Criteria

• "Active now" shows in real-time
• "Seen at [time]" shows on last read message
• Delivery status icons work (sent/delivered/read)
• Multi-device presence is tracked
• Typing indicator shows avatar