fix: ensure SSH private key has trailing newline in CI workflow

printf '%s' strips trailing newlines; use printf '%s\n' to ensure
the OpenSSH key file is well-formed and passes libcrypto validation.

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

.forgejo/workflows/deploy.yml

@@ -49,7 +49,7 @@ jobs:
       - name: Configure SSH
         run: |
           mkdir -p ~/.ssh
-          printf '%s' "${{ secrets.SSH_PRIVATE_KEY }}" > ~/.ssh/id_ed25519
+          printf '%s\n' "${{ secrets.SSH_PRIVATE_KEY }}" > ~/.ssh/id_ed25519
           chmod 600 ~/.ssh/id_ed25519
           # Scan host keys directly (no need for SSH_KNOWN_HOSTS secret)
           ssh-keyscan -p 22 87.249.49.32 >> ~/.ssh/known_hosts