feat(app): UI parity with Pencil mockup — top bar, panel cards, sidebar/event-center polish

Top bar (breadcrumb + actions + account), rounded panel cards with active
accent + rich headers, sidebar count pills/collapsible groups/daemon footer,
preset chips + scrollback pill, Event Center tabs + external-notify footer,
JetBrains Mono + Inter via @fontsource, shared theme tokens. Backend-absent
pieces are mocked (search, zoom, uptime, channels) pending SP1–SP5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main.tsx

@@ -1,7 +1,13 @@
 import React from "react";
 import ReactDOM from "react-dom/client";
 import { App } from "./App";
+import "@fontsource/inter/400.css";
+import "@fontsource/inter/500.css";
+import "@fontsource/inter/600.css";
+import "@fontsource/inter/700.css";
+import "@fontsource-variable/jetbrains-mono";
 import "@xterm/xterm/css/xterm.css";
+import "./styles.css";
 
 ReactDOM.createRoot(document.getElementById("root")!).render(
   <React.StrictMode>