feat(admin): #356 후속 — verifyAllAsync로 즉시 응답

- 1244 링크 백필 동기 호출 시 HTTP 25~30분 hang (ingress 5분 timeout 초과)
- @Async verifyAllAsync 추가, controller는 started/pending 즉시 응답
- 진행은 /api/admin/video-relevance/pending 폴링으로 확인

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend-java/src/main/java/com/tasteby/controller/AdminVideoRelevanceController.java

@@ -40,9 +40,11 @@ public class AdminVideoRelevanceController {
     @PostMapping("/all")
     public Map<String, Object> verifyAll(@RequestParam(defaultValue = "10") int batchSize) {
         var admin = AuthUtil.requireAdmin();
-        log.info("[ADMIN] {} triggered video-relevance verifyAll(batchSize={})", admin.getSubject(), batchSize);
-        int processed = relevanceService.verifyAll(batchSize);
-        return Map.of("processed", processed);
+        int pending = restaurantService.countUnevaluatedLinks();
+        log.info("[ADMIN] {} triggered video-relevance verifyAllAsync (batchSize={}, pending={})", admin.getSubject(), batchSize, pending);
+        // 비동기 트리거 — HTTP request는 즉시 응답. 진행은 /pending 폴링으로 확인.
+        relevanceService.verifyAllAsync(batchSize);
+        return Map.of("started", true, "pending", pending);
     }
 
     @PostMapping("/{linkId}/evaluate")

backend-java/src/main/java/com/tasteby/service/VideoRelevanceService.java

@@ -63,6 +63,16 @@ public class VideoRelevanceService {
         restaurantService.updateLinkRelevance(linkId, result.relevance(), truncate(result.reason(), 120));
     }
 
+    @Async
+    public void verifyAllAsync(int batchSize) {
+        try {
+            int n = verifyAll(batchSize);
+            log.info("[VideoRelevance] backfill done: {} processed", n);
+        } catch (Exception e) {
+            log.warn("verifyAllAsync failed: {}", e.getMessage());
+        }
+    }
+
     public int verifyAll(int batchSize) {
         int total = 0;
         List<Map<String, Object>> batch;