Display online status for users

[ih8js-git]

Currently, there is no indication of whether a user is online or offline in the UI.

Proposed Changes

1. WebSocket / API Support:
   • Add/handle the UserPresence event in src/api/events.rs and src/api/ws.rs (and capture presence state from the Ready payload).
   • Track user presence (online/offline status) in the state store.
2. UI Indication:
   • Display an online indicator (e.g., a green indicator ● or status icon) next to user names in the DM list (src/views/dm_list.rs), DM chat headers (src/views/dm.rs), and future member lists.