chore: remove legacy tools/codex-skills (moved to .agents/skills), split filter drawer tests, clean up stale docs

- tools/codex-skills/ removed — skills now live in .agents/skills/
- docs/reference-agents-*.md removed — replaced by .agents/workflow.md
- FilterDrawerContractTest split into Runtime + Template contract tests
- bin scripts and .gitignore updated for .agents/ paths

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -13,6 +13,10 @@ composer.phar
 config/config.php
 .env
 
+# Agent workflow runs (ephemeral artifacts)
+/.agents/runs/*
+!/.agents/runs/.gitkeep
+
 # Runtime & generated
 /web/debugger/
 /data/