fix: GitHub Actions checkout@v5 → checkout@v4 변경

v5는 인증 오류 발생, 안정 버전인 v4로 전체 워크플로우 통일

https://claude.ai/code/session_016DE3uHLsVmA5Uv7gZGGaKT

.github/workflows/build-base-image.yml

@@ -18,7 +18,7 @@ jobs:
       contents: read
       packages: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
 
       - name: GHCR 로그인
         uses: docker/login-action@v3

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
 
       - name: Python 설정
         uses: actions/setup-python@v5
@@ -46,7 +46,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
 
       - name: Python 설정
         uses: actions/setup-python@v5

.github/workflows/fly-deploy.yml

@@ -14,7 +14,7 @@ jobs:
       contents: read
       packages: read
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
 
       - name: GHCR 로그인
         uses: docker/login-action@v3

.github/workflows/hf-sync.yml

@@ -8,7 +8,7 @@ jobs:
   sync:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0