Add AGENTS.md

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dblock

AGENTS.md

@@ -0,0 +1,32 @@
+# AI Agent Instructions
+
+## After Making Code Changes
+
+Always run the following commands before committing:
+
+1. **Fix lint**: `bundle exec rubocop -a`
+2. **Update rubocop todo**: `bundle exec rubocop --auto-gen-config`
+3. **Run tests**: `bundle exec rspec`
+
+## Changelog
+
+Update [CHANGELOG.md](CHANGELOG.md) for any user-facing change. Add a line at the top under `### Changelog` in the format:
+
+```
+* YYYY/MM/DD: Description of change - [@dblock](https://github.com/dblock), [@Copilot](https://github.com/apps/copilot-swe-agent).
+```
+
+## Tests
+
+- Tests live in `spec/` and use RSpec with Fabrication for factories (`spec/fabricators/`).
+- Write tests for all new features and bug fixes.
+- Requires a local MongoDB instance (see `config/mongoid.yml`).
+
+## Code Style
+
+- Ruby style is enforced via RuboCop (`.rubocop.yml`). Persistent exceptions live in `.rubocop_todo.yml`.
+- Do not add new entries to `.rubocop_todo.yml` for code you write — fix the offenses instead.
+
+## Commits and PRs
+
+- Squash commits before merging — one logical commit per PR.