Add AGENTS.md and CLAUDE.md for AI coding agent guidance (#26)

* Add AGENTS.md and CLAUDE.md for AI coding agent guidance

* Fix inaccuracies in AGENTS.md

- Remove redundant heading that repeats the filename
- Fix incorrect spec/fixtures/ references where that directory doesn't exist
- Fix Claude-specific intro text to be agent-agnostic (pks only)

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

---------

Co-authored-by: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: dduugg

AGENTS.md

@@ -0,0 +1,30 @@
+This file provides guidance to AI coding agents when working with code in this repository.
+
+## What this project is
+
+`code_teams` is a low-dependency, plugin-based Ruby gem for declaring and querying engineering teams within a codebase. Teams are defined in `config/teams/*.yml` files, and plugins extend validation and querying behavior per organization.
+
+## Commands
+
+```bash
+bundle install
+
+# Run all tests (RSpec)
+bundle exec rspec
+
+# Run a single spec file
+bundle exec rspec spec/path/to/spec.rb
+
+# Lint
+bundle exec rubocop
+bundle exec rubocop -a  # auto-correct
+
+# Type checking (Sorbet)
+bundle exec srb tc
+```
+
+## Architecture
+
+- `lib/code_teams.rb` — public API: `CodeTeams.all`, `CodeTeams.find`, team plugin registration
+- `lib/code_teams/` — `Team` struct, YAML parsing, plugin interface, and built-in plugins
+- `spec/` — RSpec tests

CLAUDE.md

@@ -0,0 +1 @@
+@AGENTS.md