Clear lint warnings from the audit branch (deps + extract NotFound)

- CreationWizard: add sys.skills to the loader effect's deps (stable singleton).
- Extract NotFound to src/app/NotFound.tsx so router.tsx no longer trips
  react-refresh/only-export-components.

Branch is now warning-clean (the 3 remaining eslint errors are pre-existing on master,
in files this branch does not touch).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/NotFound.tsx

@@ -0,0 +1,12 @@
+import { Link } from '@tanstack/react-router';
+
+/** Shown for any URL outside the app's routes (previously rendered a blank shell). */
+export function NotFound() {
+  return (
+    <div className="p-10 text-center">
+      <h1 className="font-display text-2xl font-semibold text-ink">Page not found</h1>
+      <p className="mt-2 text-muted">That page doesn’t exist or has moved.</p>
+      <Link to="/" className="mt-4 inline-block text-accent hover:underline">Back to campaigns</Link>
+    </div>
+  );
+}