fix(ci): replace actions/checkout with manual git clone for SHA-256 repos

Gitea uses SHA-256 object hashes; actions/checkout@v4 from GitHub only
handles SHA-1 and fails to resolve the 64-char ref.  Use git clone +
git checkout directly instead.

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

.gitea/workflows/build.yml

@@ -10,7 +10,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          git clone ${{ github.server_url }}/${{ github.repository }}.git .
+          git checkout ${{ github.sha }}
 
       - name: Login to Gitea Registry
         run: |
@@ -28,7 +30,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        run: |
+          git clone ${{ github.server_url }}/${{ github.repository }}.git .
+          git checkout ${{ github.sha }}
 
       - name: Create deployment directory
         uses: appleboy/ssh-action@v1.0.3