feat(frontend): S0 Vue3 脚手架 + auth + Layout shell（4入口，模拟/实盘灰显）

- Vite+TS+ElementPlus+ECharts+Pinia+Router+Axios
- auth store + JWT axios 拦截器 + 路由守卫
- 登录页 + Layout（侧栏 4 入口，回测/投研 active，模拟/实盘 disabled）
- 占位页（backtest/factor，S1/S2 填充）
- vitest auth store 3 tests passed + build 通过(dist 生成)

frontend/tests/auth.test.ts

@@ -0,0 +1,35 @@
+import { setActivePinia, createPinia } from 'pinia'
+import { beforeEach, describe, expect, it } from 'vitest'
+import { useAuthStore } from '@/stores/auth'
+
+describe('auth store', () => {
+  beforeEach(() => {
+    localStorage.clear()
+    setActivePinia(createPinia())
+  })
+
+  it('starts unauthenticated', () => {
+    const auth = useAuthStore()
+    expect(auth.isAuthenticated).toBe(false)
+    expect(auth.token).toBe(null)
+  })
+
+  it('setToken stores token + username and authenticates', () => {
+    const auth = useAuthStore()
+    auth.setToken('jwt-xyz', 'admin')
+    expect(auth.token).toBe('jwt-xyz')
+    expect(auth.username).toBe('admin')
+    expect(auth.isAuthenticated).toBe(true)
+    expect(localStorage.getItem('token')).toBe('jwt-xyz')
+  })
+
+  it('logout clears token + username', () => {
+    const auth = useAuthStore()
+    auth.setToken('jwt-xyz', 'admin')
+    auth.logout()
+    expect(auth.token).toBe(null)
+    expect(auth.username).toBe(null)
+    expect(auth.isAuthenticated).toBe(false)
+    expect(localStorage.getItem('token')).toBe(null)
+  })
+})