IDEA-8: GraphRAG — NetworkX 기반 지식 그래프

- td_knowledge_graph 테이블 (user_id, subject, relation, object 트리플)
- GraphService: MultiDiGraph 인메모리 캐시 + MySQL 영속화
- add_relation / query_entity LangChain 도구
- call_model에 그래프 요약 자동 주입 (시스템 프롬프트)
- GRAPH_ENABLED=true 환경변수로 활성화
- requirements.txt에 networkx>=3.0 추가

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

services/db/mysql_service.py

@@ -110,6 +110,17 @@ class DatabaseService:
                 created_at DATETIME DEFAULT CURRENT_TIMESTAMP
             )
         """)
+        cursor.execute("""
+            CREATE TABLE IF NOT EXISTS td_knowledge_graph (
+                id INT AUTO_INCREMENT PRIMARY KEY,
+                user_id VARCHAR(50) NOT NULL,
+                subject VARCHAR(200) NOT NULL,
+                relation VARCHAR(100) NOT NULL,
+                object VARCHAR(200) NOT NULL,
+                created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+                INDEX idx_user_subject (user_id, subject(80))
+            )
+        """)
         cursor.execute("""
             CREATE TABLE IF NOT EXISTS td_reminders (
                 id INT AUTO_INCREMENT PRIMARY KEY,