fix: resolve Docker build failures in GitHub Actions

- Added ca-certificates package for proper SSL certificate validation
- Configured git to handle SSL and initialization properly
- Added --depth 1 for faster cloning and reduced network issues
- Improved error handling to continue build even if docs clone fails
- Fixed su-exec issue by using Alpine's native su command
- Redirected git clone stderr to avoid polluting build logs

These changes address the exit code 128 git errors occurring in GitHub Actions
Docker builds while maintaining backwards compatibility.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

docker/docker-entrypoint.sh

@@ -28,8 +28,8 @@ fi
 if [ "$(id -u)" = "0" ]; then
     echo "Running as root, fixing permissions..."
     chown -R nodejs:nodejs /app/data
-    # Switch to nodejs user
-    exec su-exec nodejs "$@"
+    # Switch to nodejs user (using Alpine's native su)
+    exec su nodejs -c "$*"
 fi
 
 # Trap signals for graceful shutdown