Add AGENTS.md and CLAUDE.md for AI coding agent guidance (#55)

* 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 +1,26 @@
+This file provides guidance to AI coding agents when working with code in this repository.
+
+## What this project is
+
+`pack_stats` collects and reports modularization statistics about a Rails application using packwerk. It sends opinionated metrics (e.g. violation counts, pack sizes, ownership breakdown) to DataDog and other observability systems.
+
+## Commands
+
+```bash
+bundle install
+
+# Run all tests (RSpec)
+bundle exec rspec
+
+# Run a single spec file
+bundle exec rspec spec/path/to/spec.rb
+
+# Type checking (Sorbet)
+bundle exec srb tc
+```
+
+## Architecture
+
+- `lib/pack_stats.rb` — entry point; `PackStats.report_to_datadog!` is the primary public method
+- `lib/pack_stats/` — metric collectors (per-pack and per-team stats), DataDog gauge/distribution reporters, and configuration
+- `spec/` — RSpec tests

CLAUDE.md

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