test(cmd): add unit tests for main.go

- Add TestFormatPorts covering empty, single, and multiple ports
- Add TestMain_VersionFlag_VerifiesOutput checking version variables
- Add TestFlagParsing verifying CLI flag parsing behavior
- Fix .gitignore to only ignore root-level binary, not cmd/ja4sentinel/

Implements testing.policy.requirements.test_skeletons from architecture.yml

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

.gitignore

@@ -52,6 +52,6 @@ test-results/
 packaging/test/*.deb
 packaging/test/*.rpm
 
-# Binary
-ja4sentinel
+# Binary (root level only)
+/ja4sentinel
 ja4sentinel-linux-amd64