feat(auth): 重构认证系统，引入 session 会话管理

- 新增 user_sessions 数据库表及 Alembic 迁移
- 实现 SessionService 会话生命周期管理（创建/刷新/撤销/清理）
- 认证流程改用 refresh token cookie + access token 双令牌模式
- 前端实现自动静默刷新、跨标签页同步及设备指纹
- 用户设置页新增会话管理和密码修改功能
- 管理员用户管理新增强制登出和会话查看
- 密码策略增强，支持强度校验和泄露检测
- OAuth 登录流程适配新会话机制
- 新增完整的单元测试和 API 测试覆盖

Closes #232

Co-authored-by: LewisPen <LewisPen@nyadoo.com>

frontend/src/api/__tests__/client.spec.ts

@@ -0,0 +1,31 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import apiClient, { AUTH_STATE_CHANGE_EVENT } from '@/api/client'
+
+describe('apiClient auth state change event', () => {
+  beforeEach(() => {
+    localStorage.clear()
+    apiClient.clearAuth()
+  })
+
+  afterEach(() => {
+    localStorage.clear()
+    apiClient.clearAuth()
+  })
+
+  it('dispatches a same-tab auth change event when clearing auth', () => {
+    const handler = vi.fn()
+    window.addEventListener(AUTH_STATE_CHANGE_EVENT, handler as EventListener)
+
+    apiClient.setToken('access-token')
+    apiClient.clearAuth()
+
+    expect(localStorage.getItem('access_token')).toBeNull()
+    expect(handler).toHaveBeenCalledTimes(1)
+
+    const event = handler.mock.calls[0][0] as CustomEvent<{ token: string | null }>
+    expect(event.detail).toEqual({ token: null })
+
+    window.removeEventListener(AUTH_STATE_CHANGE_EVENT, handler as EventListener)
+  })
+})