feat: RAG 임베딩 자동 동기화 + AI 서비스 개선

- 부적합 라이프사이클 전 과정에서 Qdrant 임베딩 자동 동기화
  - 관리함 5개 저장 함수 + 수신함 상태 변경 시 fire-and-forget sync
  - 30분 주기 전체 재동기화 안전망 (FastAPI lifespan 백그라운드 태스크)
  - build_document_text에 카테고리(final_category/category) 포함
- RAG 질의에 DB 통계 집계 지원 (카테고리별/부서별 건수)
- Qdrant client.search → query_points API 마이그레이션
- AI 어시스턴트 페이지 권한 추가 (tkuser)

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

ai-service/services/db_client.py

@@ -82,6 +82,38 @@ def get_daily_qc_stats(date_str: str) -> dict:
         return dict(row._mapping) if row else {}
 
 
+def get_category_stats() -> list[dict]:
+    """카테고리별 부적합 건수 집계"""
+    with engine.connect() as conn:
+        result = conn.execute(
+            text(
+                "SELECT COALESCE(final_category, category) AS category, "
+                "COUNT(*) AS count "
+                "FROM qc_issues "
+                "GROUP BY COALESCE(final_category, category) "
+                "ORDER BY count DESC"
+            )
+        )
+        return [dict(row._mapping) for row in result]
+
+
+def get_department_stats() -> list[dict]:
+    """부서별 부적합 건수 집계"""
+    with engine.connect() as conn:
+        result = conn.execute(
+            text(
+                "SELECT responsible_department AS department, "
+                "COUNT(*) AS count "
+                "FROM qc_issues "
+                "WHERE responsible_department IS NOT NULL "
+                "AND responsible_department != '' "
+                "GROUP BY responsible_department "
+                "ORDER BY count DESC"
+            )
+        )
+        return [dict(row._mapping) for row in result]
+
+
 def get_issues_for_date(date_str: str) -> list[dict]:
     with engine.connect() as conn:
         result = conn.execute(