feat(P2): 实现质量保障类5项功能(无障碍/视觉回归/通知渠道/漏洞扫描/灾备)

## 新增功能

### 1. 屏幕阅读器兼容性增强（a11y）
- 无障碍工具库：src/shared/lib/a11y.ts
- aria-live Hook：src/shared/hooks/use-aria-live.ts
- a11y 组件：skip-link/visually-hidden/focus-trap/aria-status
- 增强 UI：table.tsx 系统性 ARIA role，dialog.tsx aria-modal
- 审计文档：docs/accessibility/a11y-audit.md（WCAG 2.1 AA 清单）

### 2. 视觉回归测试
- 测试套件：tests/visual/（homepage + 3 个 dashboard）
- 3 视口（desktop/tablet/mobile）× 2 主题（light/dark）
- 动态元素遮罩，避免误报
- playwright.config.ts 新增 visual-chromium 项目
- 文档：docs/testing/visual-regression.md

### 3. 短信/微信推送渠道集成
- 新模块：src/modules/notifications/
- 4 个渠道：SMS（阿里云/腾讯云）、WeChat（公众号）、Email（SMTP）、In-App
- 分发器按用户偏好并行多渠道发送
- 外部 SDK 动态 import，Mock 模式开发可用
- 文档：docs/notifications/channels.md

### 4. 漏洞扫描 CI 集成
- CI security-scan job：npm audit + Snyk + Trivy FS + OWASP ZAP
- 独立工作流 security.yml：每周一深度扫描 + 容器镜像扫描
- 配置：suppressions.json + .trivyignore
- 本地脚本：security-scan.sh/ps1
- 文档：docs/security/scanning.md（SLA 分级）

### 5. 灾备方案
- 脚本：backup-verify/backup-offsite-sync/dr-drill/failover/health-check
- CI 增强：备份后校验+异地同步，每周灾备演练
- 独立工作流 dr-drill.yml：每周一凌晨 4 点自动演练
- 文档：docs/dr/dr-plan.md（RTO 4h/RPO 24h）+ dr-runbook.md（6 故障场景）

## 验证
- npx tsc --noEmit：0 错误
- npm run lint：0 错误 0 警告

tests/visual/admin-dashboard.spec.ts

@@ -0,0 +1,67 @@
+import { expect, test } from "@playwright/test"
+import { setupAuthState } from "./helpers/auth"
+import { buildMaskOption, maskDynamicElements, setTheme, setViewport, waitForPageReady } from "./helpers/visual-helpers"
+import { SCREENSHOT_DEFAULT_OPTIONS, THEMES, VIEWPORT_LIST, snapshotName } from "./visual.config"
+
+/**
+ * 管理员仪表盘视觉回归测试
+ *
+ * 登录后访问 /admin/dashboard,在 desktop/tablet/mobile 三种视口
+ * 以及 light/dark 两种主题下进行整页快照,
+ * 并单独对侧边栏与主内容区做组件级快照。
+ *
+ * 需要数据库环境以完成登录流程;未配置 DATABASE_URL 时自动跳过。
+ */
+test.describe("Admin dashboard visual regression", () => {
+  test.skip(!process.env.DATABASE_URL, "requires DATABASE_URL for authenticated visual tests")
+
+  for (const viewport of VIEWPORT_LIST) {
+    for (const theme of THEMES) {
+      test(`admin-dashboard @ ${viewport} @ ${theme}`, async ({ page }) => {
+        await setViewport(page, viewport)
+        await setTheme(page, theme)
+        await setupAuthState(page, "admin")
+        await page.goto("/admin/dashboard")
+        await waitForPageReady(page)
+
+        const masks = await maskDynamicElements(page, ["[data-testid='stat-card-value']", "[data-testid='chart']"])
+        await expect(page).toHaveScreenshot(snapshotName("admin-dashboard", viewport, theme), {
+          ...SCREENSHOT_DEFAULT_OPTIONS,
+          ...buildMaskOption(masks),
+        })
+      })
+    }
+  }
+
+  test("admin-dashboard sidebar component @ desktop @ light", async ({ page }) => {
+    test.skip(!process.env.DATABASE_URL, "requires DATABASE_URL for authenticated visual tests")
+    await setViewport(page, "desktop")
+    await setTheme(page, "light")
+    await setupAuthState(page, "admin")
+    await page.goto("/admin/dashboard")
+    await waitForPageReady(page)
+
+    const sidebar = page.locator("[data-testid='sidebar'], aside, nav").first()
+    const masks = await maskDynamicElements(page)
+    await expect(sidebar).toHaveScreenshot("admin-dashboard-sidebar-desktop-light.png", {
+      ...SCREENSHOT_DEFAULT_OPTIONS,
+      ...buildMaskOption(masks),
+    })
+  })
+
+  test("admin-dashboard main content @ desktop @ light", async ({ page }) => {
+    test.skip(!process.env.DATABASE_URL, "requires DATABASE_URL for authenticated visual tests")
+    await setViewport(page, "desktop")
+    await setTheme(page, "light")
+    await setupAuthState(page, "admin")
+    await page.goto("/admin/dashboard")
+    await waitForPageReady(page)
+
+    const main = page.locator("main").first()
+    const masks = await maskDynamicElements(page, ["[data-testid='stat-card-value']", "[data-testid='chart']"])
+    await expect(main).toHaveScreenshot("admin-dashboard-main-desktop-light.png", {
+      ...SCREENSHOT_DEFAULT_OPTIONS,
+      ...buildMaskOption(masks),
+    })
+  })
+})