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/vite.config.ts

@@ -0,0 +1,22 @@
+import { defineConfig } from 'vite';
+import { svelte } from '@sveltejs/vite-plugin-svelte';
+
+// In dev, API calls are proxied to a locally running panel (cargo run -p scopenet-panel).
+const target = process.env.PANEL_URL ?? 'http://localhost:8080';
+
+export default defineConfig({
+  plugins: [svelte()],
+  server: {
+    port: 5173,
+    proxy: {
+      '/api': target,
+      '/files': target,
+      '/uploads': target,
+    },
+  },
+  build: {
+    target: 'es2022',
+    cssCodeSplit: false,
+    chunkSizeWarningLimit: 800,
+  },
+});