refactor: shared 모듈 추출 Phase 1~4 (notifyHelper, errors, logger, auth, dbPool)

Phase 1: notifyHelper.js → shared/utils/ (4개 서비스 중복 제거)
Phase 2: auth.js → shared/middleware/ (system1/system2 통합)
Phase 3: errors.js + logger.js → shared/utils/ (system1/system2 통합)
Phase 4: DB pool → shared/config/database.js (Group B 4개 서비스 통합)

- Docker 빌드 컨텍스트를 루트로 변경 (6개 API 서비스)
- 기존 파일은 re-export 패턴으로 consumer 변경 0개 유지
- .dockerignore 추가로 빌드 최적화

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

docker-compose.yml

@@ -80,8 +80,8 @@ services:
 
   system1-api:
     build:
-      context: ./system1-factory/api
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: system1-factory/api/Dockerfile
     container_name: tk-system1-api
     restart: unless-stopped
     ports:
@@ -152,8 +152,8 @@ services:
 
   system2-api:
     build:
-      context: ./system2-report/api
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: system2-report/api/Dockerfile
     container_name: tk-system2-api
     restart: unless-stopped
     ports:
@@ -252,8 +252,8 @@ services:
 
   tkuser-api:
     build:
-      context: ./user-management/api
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: user-management/api/Dockerfile
     container_name: tk-tkuser-api
     restart: unless-stopped
     ports:
@@ -302,8 +302,8 @@ services:
 
   tkpurchase-api:
     build:
-      context: ./tkpurchase/api
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: tkpurchase/api/Dockerfile
     container_name: tk-tkpurchase-api
     restart: unless-stopped
     ports:
@@ -343,8 +343,8 @@ services:
 
   tksafety-api:
     build:
-      context: ./tksafety/api
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: tksafety/api/Dockerfile
     container_name: tk-tksafety-api
     restart: unless-stopped
     ports:
@@ -388,8 +388,8 @@ services:
 
   tksupport-api:
     build:
-      context: ./tksupport/api
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: tksupport/api/Dockerfile
     container_name: tk-tksupport-api
     restart: unless-stopped
     ports: