feat: standalone web UI (React + Vite)

React + TypeScript UI on port 5274. Connects to local daemon via
WebSocket IPC (DaemonAdapter). Full chat layout with sidebar, message
pane, and peer list. Mirrors the TUI feature set.

- src/types.ts        — IPC types mirroring proto.go
- src/adapter/daemon  — WebSocket IPC adapter with auto-reconnect
- src/store/index.ts  — Zustand store; handles all daemon events
- src/pages/          — Onboarding (connect + join) and Chat
- src/components/     — Sidebar, MessagePane, PeerList

Dev: cd web && npm run dev  (port 5274)
Build: cd web && npm run build

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

web/src/pages/Chat.tsx

@@ -0,0 +1,13 @@
+import { Sidebar } from '../components/Sidebar'
+import { MessagePane } from '../components/MessagePane'
+import { PeerList } from '../components/PeerList'
+
+export function Chat() {
+  return (
+    <div className="chat-layout">
+      <Sidebar />
+      <MessagePane />
+      <PeerList />
+    </div>
+  )
+}