feat(backend): #357 DDG → Naver Search 정식 API + DDG 폴백

- WebSearchService 신규 (Naver webkr.json 우선, 키 미설정/실패 시 DDG)
- RestaurantController.searchTabling/searchCatchtable 내부 호출 교체
- 인라인 DDG 80줄 제거, 미사용 import 정리
- app.naver.client-id/secret 추가 (env: NAVER_CLIENT_ID/SECRET)
- k8s secrets template에 NAVER 키 항목

Refs: #357 (close)

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

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

k8s/secrets.yaml.template

@@ -9,9 +9,12 @@ type: Opaque
 stringData:
   ORACLE_USER: "<oracle-username>"
   ORACLE_PASSWORD: "<oracle-password>"
-  ORACLE_DSN: "<tns-alias>_high?TNS_ADMIN=/etc/oracle/wallet"
+  ORACLE_DSN: "<tns-alias>_medium?TNS_ADMIN=/etc/oracle/wallet"
   JWT_SECRET: "<jwt-secret>"
   OCI_COMPARTMENT_ID: "<oci-compartment-id>"
   OCI_CHAT_MODEL_ID: "<oci-chat-model-id>"
   GOOGLE_MAPS_API_KEY: "<google-maps-api-key>"
   YOUTUBE_DATA_API_KEY: "<youtube-data-api-key>"
+  # #357 — Naver Search API (선택). 미설정 시 DDG 폴백.
+  NAVER_CLIENT_ID: "<naver-client-id>"
+  NAVER_CLIENT_SECRET: "<naver-client-secret>"