feat(c2): ADR-073-C C2 — 前端飛輪 KPI 元件接真實 API

- 新增 FlywheelKPICard 元件
- 消費 GET /api/v1/stats/summary，30 秒輪詢
- 顯示 Playbooks、修復成功率、今日轉化數、KM 向量化率
- 卡住 Incident 警示條
- 插入首頁右欄 PendingApprovalsCard 之後

2026-04-12 ogt (ADR-073-C C2)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/app/[locale]/page.tsx

@@ -32,6 +32,7 @@ import { DispositionMini } from '@/components/shared/disposition-mini'
 import { RecentActivity } from '@/components/shared/recent-activity'
 import { PendingApprovalsCard } from '@/components/shared/pending-approvals-card'
 import { AIModelStatus } from '@/components/shared/ai-model-status'
+import { FlywheelKPICard } from '@/components/dashboard/flywheel-kpi-card'
 
 const API_BASE = process.env.NEXT_PUBLIC_API_URL ?? ''
 
@@ -924,6 +925,9 @@ export default function Home({ params }: { params: { locale: string } }) {
             {/* 待審批任務 (S7) */}
             <PendingApprovalsCard />
 
+            {/* 飛輪健康度 KPI (ADR-073-C C2) */}
+            <FlywheelKPICard />
+
             {/* 基礎架構 — Toggle: 拓撲圖 / 主機網格 */}
             <div style={{
               background: '#fff',