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>

web/src/App.css

@@ -49,9 +49,11 @@ details summary { color: var(--muted); font-size: 12px; cursor: pointer; }
 
 /* ── sidebar ── */
 .sidebar { background: var(--surface); border-right: 1px solid var(--border); display: flex; flex-direction: column; overflow-y: auto; }
-.sidebar-identity { padding: 12px 12px 10px; border-bottom: 1px solid var(--border); }
+.sidebar-identity { padding: 12px 12px 10px; border-bottom: 1px solid var(--border); display: flex; align-items: center; gap: 6px; }
 .sidebar-identity .alias { display: block; font-weight: 600; font-size: 14px; }
 .sidebar-identity .peer-id { display: block; color: var(--muted); font-size: 10px; font-family: monospace; margin-top: 2px; }
+.sidebar-logout { background: none; color: var(--muted); font-size: 14px; padding: 2px 4px; flex-shrink: 0; margin-left: auto; }
+.sidebar-logout:hover { color: #e06060; background: none; }
 .sidebar-section { display: flex; flex-direction: column; padding: 8px 0; border-bottom: 1px solid var(--border); }
 .sidebar-section:last-child { border-bottom: none; flex: 1; }
 .sidebar-label { font-size: 10px; text-transform: uppercase; letter-spacing: 0.1em; color: var(--muted); padding: 4px 12px 2px; }