feat: session persistence, logout button, TURN HMAC fix; update docs

- Browser mode auto-rejoins saved network on reload (waste_last_network)
- Logout button (⏻) in sidebar clears session; optionally clears identity keypair
- TURN credentials now use HMAC-SHA1 of username (coturn use-auth-secret compatible)
- README: deploy scripts documented, session persistence section, serve-web.sh noted
- FUTURE.md: mark shipped items, add remaining work for daemon TURN + TUI rooms

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/settings.json

@@ -1,7 +1,9 @@
 {
   "permissions": {
     "allow": [
-      "Bash(go build *)"
+      "Bash(go build *)",
+      "Bash(npx tsc *)",
+      "Bash(npm run *)"
     ]
   }
 }