Stop tracking macOS .DS_Store files

Finder metadata was tracked at the repository root and nearly got
packaged inside the integration. Ignore .DS_Store everywhere, untrack
the root copy (the local file stays) and make the package check reject
it under custom_components.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -4,3 +4,4 @@ __pycache__/
 .coverage
 htmlcov/
 .venv/
+.DS_Store