Introduce AGENTS.md with dcat workflow, .gitattributes merge driver for
dcat JSONL files, and .dogcats/ config + empty issue store. Update
CLAUDE.md to point agents at AGENTS.md and avoid the TodoWrite tool, and
ignore local-only dcat files (config.local.toml, .issues.lock).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
