Fix markdown lint errors and address review feedback

- Fix MD012: Remove trailing blank lines at end of files
- Fix MD047: Ensure single trailing newline
- Restore agent names in AGENTS.md files
- Replace get-github-token.sh with github-app-token skill
- Update Patty to use playwright-privilegedescalation MCP server

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

regression-regina/HEARTBEAT.md

@@ -95,4 +95,3 @@ For each open bug:
 - Attempt to reproduce in the current codebase
 - If reproducible: comment with exact steps and assign to the relevant engineer
 - If not reproducible: comment noting what you tried and ask for clarification
-