Update .gitignore: exclude GITHUB_METADATA.md

- GITHUB_METADATA.md is a local setup guide, not needed in repo
- Keep CRITICAL_PATCH_COMPLETE.md (referenced in README)

Author: Flamehaven Labs

.gitignore

@@ -57,3 +57,6 @@ RELEASE_v*.md
 certification_report.md
 SLOPPYLINT_COMPARISON.md
 tests/manual_test/*.md
+
+# Development artifacts
+GITHUB_METADATA.md