sync: add AI review pipeline, parallel skill-files fetch, Redis cache improvements

- feat(review): add skill_reviews table, review API endpoints (pending/submit/stats), admin auth
- perf: parallel file fetching in skill-files API (was sequential → timeout)
- fix: handle Date serialization from Redis cache
- fix: align curation batch scripts with current browseReadyFilter

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

apps/web/app/api/review/stats/route.ts

@@ -0,0 +1,79 @@
+import { type NextRequest, NextResponse } from 'next/server';
+import { createDb, skillReviewQueries } from '@skillhub/db';
+import { requireAdmin } from '@/lib/admin-auth';
+import { withRateLimit, createRateLimitResponse, createRateLimitHeaders } from '@/lib/rate-limit';
+import { getCached, setCache, cacheKeys, cacheTTL } from '@/lib/cache';
+
+const db = createDb();
+
+interface ReviewStatsData {
+  unreviewed: number;
+  auto_scored: number;
+  ai_reviewed: number;
+  verified: number;
+  needs_re_review: number;
+  total_reviews: number;
+}
+
+/**
+ * GET /api/review/stats
+ * Returns review pipeline status statistics.
+ */
+export async function GET(request: NextRequest) {
+  // Rate limiting
+  const rateLimitResult = await withRateLimit(request, 'anonymous');
+  if (!rateLimitResult.allowed) {
+    return createRateLimitResponse(rateLimitResult);
+  }
+
+  // Admin check (supports API key auth via Authorization header)
+  const adminCheck = await requireAdmin(request);
+  if (!adminCheck.authorized) {
+    return adminCheck.response;
+  }
+
+  try {
+    // Check cache
+    const cacheKey = cacheKeys.reviewStats();
+    const cached = await getCached<ReviewStatsData>(cacheKey);
+    if (cached) {
+      return NextResponse.json(cached, {
+        headers: {
+          'X-Cache': 'HIT',
+          ...createRateLimitHeaders(rateLimitResult),
+        },
+      });
+    }
+
+    // Run stats and total reviews count in parallel
+    const [statusCounts, totalReviews] = await Promise.all([
+      skillReviewQueries.getStats(db),
+      skillReviewQueries.countTotalReviews(db),
+    ]);
+
+    const data: ReviewStatsData = {
+      unreviewed: statusCounts['unreviewed'] ?? 0,
+      auto_scored: statusCounts['auto-scored'] ?? 0,
+      ai_reviewed: statusCounts['ai-reviewed'] ?? 0,
+      verified: statusCounts['verified'] ?? 0,
+      needs_re_review: statusCounts['needs-re-review'] ?? 0,
+      total_reviews: totalReviews,
+    };
+
+    // Cache for 60 seconds
+    await setCache(cacheKey, data, cacheTTL.reviewStats);
+
+    return NextResponse.json(data, {
+      headers: {
+        'X-Cache': 'MISS',
+        ...createRateLimitHeaders(rateLimitResult),
+      },
+    });
+  } catch (error) {
+    console.error('[Review] Error fetching stats:', error);
+    return NextResponse.json(
+      { error: 'Failed to fetch review stats' },
+      { status: 500 }
+    );
+  }
+}