chore: enforce zero-warning toolchain

- Enable noUnusedLocals/noUnusedParameters in tsconfig (unused code = error)
- Remove unused React import in scroll-area (caught by strict unused checks)
- Pin NODE_ENV=development for dev script (box shell leaks NODE_ENV=production,
  which made next dev emit a non-standard-env warning)

package.json

@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "private": true,
   "scripts": {
-    "dev": "next dev",
+    "dev": "NODE_ENV=development next dev",
     "build": "next build",
     "start": "next start",
     "lint": "eslint",