docs: add CLAUDE.md for Claude Code guidance

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Overview
+
+GitHub Action (TypeScript/Bun) that syncs GitHub pull requests to Asana tasks via rule-based automation. Entry point: `src/index.ts`. Built output in `dist/` is committed and used directly by the action runtime.
+
+## Essential Commands
+
+- `bun test` - Run tests
+- `bun test --watch` - Watch mode
+- `bun run package` - Bundle to dist/index.js (esbuild)
+- `bun run build` - Type-check only (tsc)
+- `bun run lint` - Lint
+- `bun run lint:fix` - Lint with fixes
+- `bun run format` - Format (prettier)
+- `bun run all` - Format, lint, test, package
+
+## Project Structure
+
+```
+src/
+  index.ts              Action entry point
+  types.ts              Shared types
+  rules/                Rule engine
+    engine.ts           Evaluates rules against PR events
+    validator.ts        Validates rule config
+    types.ts
+  expression/           Condition expression evaluation
+    evaluator.ts
+    context.ts          PR context builder
+    helpers.ts
+  util/
+    asana/              Asana API client
+      client.ts
+      create.ts         Task creation
+      update.ts         Field updates
+      tasks.ts          Task lookup
+      fields.ts         Custom field resolution
+    config.ts           Action input parsing
+    github.ts           GitHub API helpers
+    parser.ts           YAML rules parser
+    retry.ts            Retry logic
+    template-analysis.ts  Handlebars template utilities
+__tests__/              Tests mirror src/ structure
+  rules/
+  util/
+  integration/
+dist/                   Bundled output — commit after packaging
+docs/                   VitePress user-facing documentation
+```
+
+## User-Facing Documentation
+
+The `docs/` directory contains VitePress documentation for action users. Read these before implementing or modifying features:
+
+- `docs/concepts/` - Rules, conditions, actions, templates (domain model)
+- `docs/reference/` - All conditions, actions, context variables, validation rules
+- `docs/examples/` - Real-world workflows that illustrate expected behavior
+
+## Development Practices
+
+- Run `bun run all` before committing to ensure formatting, lint, tests, and packaging are all clean.
+- `dist/index.js` must be committed — the action references it directly, not a build step.
+- The action never throws or fails CI. All errors are caught and logged; workflows always continue.
+- `dry_run` mode must be respected throughout — check `src/util/config.ts` for the flag.
+- Tests use Bun's built-in test runner with msw for HTTP mocking. See `__tests__/setup.ts` for test setup.
+- Do not review or edit files in `dist/`.