- friends.js: add unmountFriends() to clear refresh/invite timers
- play/mod.js: register unmountLobby for game-lobby scene
- social/mod.js: register unmountFriends for friends scene
- net.js: add 10s request timeout via AbortController
- net.js: add mutex for token refresh (prevents duplicate refresh calls)
- notifications.js: don't auto-mark-read on mount; add explicit button
- chat.js: pass lastTime as 'after' param for incremental fetch

Fixes WTF #38, #63, #66, #69, #91, #175
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>