fix: add VERSION ARG to rpm-builder stage to fix RPM build cache issue

- Declare ARG VERSION in rpm-builder stage for FPM to access
- Add packages/ directory to .gitignore (build artifacts)

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

.gitignore

@@ -51,6 +51,9 @@ test-results/
 # Test artifacts
 packaging/test/*.rpm
 
+# Build artifacts
+packages/
+
 # Binary (root level only)
 /ja4sentinel
 ja4sentinel-linux-amd64