#23371: chore: add agentlint/prguard/secretmap skills + gitignore restart.sh

Split from #23186. ## Changes - Add three new skill definitions: agentlint, prguard, secretmap - Exclude restart.sh from git tracking via .gitignore <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds three new skill definitions (`agentlint`, `prguard`, `secretmap`) and excludes `restart.sh` from git tracking. All skills follow the established SKILL.md format with proper frontmatter (name, description, homepage, metadata) and include clear usage examples. The `.gitignore` addition prevents a local utility script from being committed. <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - it only adds documentation files and a gitignore entry - All changes are documentation-only (skill definitions) and a standard gitignore addition. No code changes, no logic modifications, no potential for runtime errors. The skill definitions follow existing patterns correctly. - No files require special attention _{Last reviewed commit: 07e0cd5} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->