Add admin panel web UI (Svelte 5)

Dashboard with launch stats, instance manager with Modrinth/CurseForge
search and zip import, player and group management, launcher design
editor with live preview, and sign-in settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011ARcGWxLx21FwXJ3yfGriS

panel/web/src/main.ts

@@ -0,0 +1,11 @@
+import '@fontsource-variable/outfit';
+import '@fontsource-variable/jetbrains-mono';
+// Launcher fonts, so the design preview matches exactly.
+import '@fontsource-variable/inter';
+import '@fontsource-variable/space-grotesk';
+import '@fontsource-variable/plus-jakarta-sans';
+import './app.css';
+import { mount } from 'svelte';
+import App from './App.svelte';
+
+mount(App, { target: document.getElementById('app')! });