Add the admin panel scaffold

A self-contained template: an Express backend with login, JWT, rate limiting
and SPA serving, and a React 18 + Vite shell with the same tab registry and
warm Material 3 design system the panel uses. No domain logic — routes and tabs
are meant to be hung off it.

node_modules and the frontend build stay out through the existing ignores.

admin/frontend/tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "lib": ["ES2020", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "jsx": "react-jsx",
+    "strict": true,
+    "skipLibCheck": true,
+    "noEmit": true,
+    "esModuleInterop": true,
+    "resolveJsonModule": true
+  },
+  "include": ["src", "vite.config.ts"]
+}