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)

tsconfig.json

@@ -5,6 +5,8 @@
     "allowJs": true,
     "skipLibCheck": true,
     "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
     "noEmit": true,
     "esModuleInterop": true,
     "module": "esnext",