fix: clean up token refresh listeners

[saurabhhhcodes]

Summary

• make addTokenRefreshListener return an unsubscribe cleanup function
• remove the active MessageContext token-refresh listener when its socket lifecycle ends
• prevent remount/login cycles from accumulating duplicate socket reconnect callbacks

Closes #196

Validation

• npm install --ignore-scripts in frontend
• git diff --check

Notes

• npm run build and npx tsc --noEmit currently reach pre-existing type errors unrelated to this listener cleanup: optional currentUser.id in MessageContext, markAllAsSeen returning void, and ChatSidebar selectedUser missing unread. I left those broader typing fixes out to keep this PR focused on the listener leak.

[vercel]

Someone is attempting to deploy a commit to the Sameer's projects Team on Vercel.

A member of the Team first needs to authorize it.