Add AGENTS.md and CLAUDE.md for AI coding agent guidance (#98)

* 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 +1,38 @@
+This file provides guidance to AI coding agents when working with code in this repository.
+
+## What this project is
+
+`codeowners-rs` is a Rust implementation of a CODEOWNERS resolver. It parses CODEOWNERS files and determines ownership of files in a repository, used as both a library and CLI tool.
+
+## Commands
+
+```bash
+# Build
+cargo build
+cargo build --release
+
+# Run all tests
+cargo test
+
+# Run a single test by name
+cargo test test_name
+
+# Lint
+cargo clippy --all-targets --all-features
+cargo fmt --all -- --check   # check only
+cargo fmt --all               # apply formatting
+
+# Check compilation without building
+cargo check
+```
+
+## Architecture
+
+- `src/main.rs` — CLI entry point using `clap`
+- `src/lib.rs` — library root; exposes the public API
+- `src/ownership.rs` / `src/ownership/` — core ownership resolution logic: parses CODEOWNERS patterns and matches them against file paths
+- `src/config.rs` — configuration loading
+- `src/runner/` — orchestrates file walking and ownership resolution
+- `src/cache/` — caching layer for resolved ownership results
+- `src/cli.rs` — CLI command definitions
+- Integration tests in `src/common_test.rs`; fixture data used in tests lives alongside test files

CLAUDE.md

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