Add regression coverage for auth store session persistence

## Problem
The current test suite does not cover auth store session persistence.

## Expected behavior
- A focused Vitest case locks the existing behavior.
- The targeted test file passes and fails if the covered behavior regresses.

## Scope
Only add regression coverage for $(@{Slug=auth-store; Focus=auth store session persistence; PrTitle=test(auth-store): cover auth session persistence; TestFile=web/src/stores/__tests__/authStore.test.ts; Mode=new; Append=/*
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import { afterEach, describe, expect, it } from 'vitest';
import useAuthStore from '../authStore';

describe('authStore', () => {
afterEach(() => {
useAuthStore.getState().logout();
localStorage.clear();
});

it('updates the in-memory session through login and logout', () => {
useAuthStore.getState().login('studio-admin', 7, true);
expect(useAuthStore.getState()).toMatchObject({
user: 'studio-admin',
userId: 7,
admin: true,
});

useAuthStore.getState().logout();
expect(useAuthStore.getState()).toMatchObject({
user: null,
userId: null,
admin: null,
});
});

it('persists display identity without a bearer token', () => {
useAuthStore.getState().login('studio-admin', 7, true);

expect(localStorage.getItem('rocketmq-studio-user')).toBe('studio-admin');
expect(localStorage.getItem('rocketmq-studio-user-id')).toBe('7');
expect(localStorage.getItem('rocketmq-studio-user-admin')).toBe('true');
expect(localStorage.getItem('token')).toBeNull();
});
});}.TestFile). No runtime behavior changes.

## Acceptance criteria
- [ ] The targeted Vitest file passes.
- [ ] git diff --check is clean.

Start with web/src/stores/__tests__/authStore.test.ts and run the targeted Vitest file. Check the existing authStore login/logout behavior and session-persistence assertions; done means the focused test passes and git diff --check is clean.

Written by the indexing model from the issue text.