chore: 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.
+
+## Development
+
+- Setup: `mise install && pnpm i`
+- Build: `pnpm build` (bundles into dist/ via @vercel/ncc)
+- Test: `pnpm test` (vitest), single file: `pnpm vitest run src/<file>.test.ts`
+- Lint: `pnpm lint`
+- Format: `pnpm format` (eslint --fix + prettier)
+- Typecheck: `pnpm typecheck`
+- Generate: `pnpm generate` (docs, inputs, unicode-regex + format)
+
+## Important: dist/ and Generated Files
+
+`dist/` is committed to the repository (required for GitHub Actions). CI verifies that `dist/` matches the build output and generated files have no drift.
+
+After changes:
+
+1. Run `pnpm build` to rebuild dist/
+2. Run `pnpm generate` if you modified action.yaml inputs, unicode handling, or documentation
+3. Commit the updated dist/ and any generated file changes
+
+## Code Style
+
+- Prefer `type` over `interface` for TypeScript type definitions
+- Use parjs (parser combinator library) for parsing logic, not regex
+- ESM modules (`"type": "module"`)
+- Conventional commits enforced via commitlint
+- Prettier: 120 char width, single quotes, trailing commas
+
+## Language
+
+All source code, comments, commit messages, and documentation must be written in English.