feat(web): add login and register pages with auth store

- API client with token refresh interceptor
- Auth API functions (login, register, logout, getMe)
- Auth store with Zustand persistence
- Auth layout with centered card design
- Login page with form validation
- Register page with company and user data
- Environment example file

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/app/(auth)/layout.tsx

@@ -0,0 +1,11 @@
+export default function AuthLayout({
+  children,
+}: {
+  children: React.ReactNode;
+}) {
+  return (
+    <div className="min-h-screen flex items-center justify-center bg-gradient-to-b from-background to-muted p-4">
+      <div className="w-full max-w-md">{children}</div>
+    </div>
+  );
+}