docs: add CLAUDE.md project instructions

Co-Authored-By: Virgil <virgil@lethean.io>

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.
+
+## Project Overview
+
+Composer library (`lthn/php-plug-business`) providing business platform integrations for the Plug framework. Currently implements Google My Business API. Licensed under EUPL-1.2.
+
+## Commands
+
+```bash
+composer install          # Install dependencies
+composer dump-autoload    # Regenerate autoloader after adding classes
+```
+
+No test suite is configured in this repository. No linter/formatter config present.
+
+## Architecture
+
+This is a **Plug provider package** — part of the `lthn/php` (core Plug framework) ecosystem. Each platform integration follows a consistent class-per-operation pattern.
+
+### Plug Framework Pattern
+
+Every operation class uses three traits from `Core\Plug\Concern\` and implements one contract from `Core\Plug\Contract\`:
+
+| Trait | Purpose |
+|-------|---------|
+| `BuildsResponse` | Wraps results into `Core\Plug\Response` objects (`ok()`, `error()`, `fromHttp()`) |
+| `ManagesTokens` | Stores/retrieves OAuth tokens via `withToken()` / `accessToken()` |
+| `UsesHttp` | Provides Laravel HTTP client via `http()` |
+
+| Contract | Method | Used by |
+|----------|--------|---------|
+| `Authenticable` | `getAuthUrl()`, `requestAccessToken()` | Auth |
+| `Refreshable` | `refresh()` | Auth |
+| `Postable` | `publish()` | Post |
+| `Listable` | `listEntities()` | Locations |
+| `Readable` | `get()`, `me()`, `list()` | Read |
+| `Deletable` | `delete()` | Delete |
+
+### Adding a New Platform
+
+Create a new directory under `src/` (e.g., `src/Yelp/`) with classes following the same trait+contract pattern. Each class should use `BuildsResponse`, `ManagesTokens`, and `UsesHttp`, and implement the appropriate contract.
+
+### Namespace
+
+`Core\Plug\Business\` maps to `src/` via PSR-4 autoloading. Requires PHP 8.2+.
+
+## Conventions
+
+- `declare(strict_types=1)` on every file
+- All public API methods return `Core\Plug\Response` (except static helpers like `getAuthUrl()`, `externalAccountUrl()`)
+- Token-dependent methods check `$this->accessToken()` first and return `$this->error()` if missing
+- Google API responses are normalized through `$this->fromHttp($response, fn ($data) => [...])` callbacks
+- Uses Laravel HTTP client (via `UsesHttp` trait) and `Illuminate\Support\Collection` for media