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.
+
+## Commands
+
+```bash
+# Build & package plugin to dist/
+make build
+
+# Run all tests (JS + PHP)
+make test
+
+# Individual test suites
+make test-js          # Jest
+make test-php         # PHPUnit in Docker
+
+# Linting
+make lint             # ESLint + StyleLint
+
+# JS asset development
+npm run start         # webpack watch (gpse/src/ → gpse/build/)
+
+# Local WordPress environment
+npm run env:start     # Start wp-env (PHP 8.2)
+npm run env:stop      # Stop wp-env
+```
+
+`make test-php` spins up `docker-compose.test.yml` (PHP 8.5 + MySQL 9.7) — Docker must be running.
+
+Run a single PHP test class: `make test-php` targets the full suite; to run one class pass it via phpunit directly inside the container or use `npm run test:php -- --filter ClassName`.
+
+## Architecture
+
+WordPress plugin that intercepts native WP search and redirects to a Google Programmable Search Engine (CSE) results page.
+
+**Entry point**: `gpse/gpse.php` — defines constants, fires `plugins_loaded` to initialize all classes.
+
+**Four PHP classes** (no namespaces; WP_ prefix convention):
+
+| Class | File | Responsibility |
+|-------|------|----------------|
+| `WP_GPSE_Admin` | `gpse/includes/class-wp-gpse-admin.php` | Settings page under Settings > GPSE; registers three options: `wp_gpse_cx_id`, `wp_gpse_results_page_id`, `wp_gpse_autocomplete_margin` |
+| `WP_GPSE_Frontend` | `gpse/includes/class-wp-gpse-frontend.php` | Search redirect via `template_redirect`; `[gpse_results]` shortcode; enqueues Google CSE script + plugin styles |
+| `WP_GPSE_Blocks` | `gpse/includes/class-wp-gpse-blocks.php` | Registers `gpse/search-results` Gutenberg block (Block API v3, server-side dynamic) |
+| `WP_GPSE_Helpers` | `gpse/includes/class-wp-gpse-helpers.php` | Static utilities for CSE HTML markup — shared between shortcode and block to avoid duplication |
+
+**Frontend flow**: WP search → `template_redirect` redirects `/?s=query` to results page with `?q=query` → results page renders `[gpse_results]` shortcode or the GPSE Gutenberg block → Google CSE JS populates results using the configured CX ID.
+
+**JS/React**: Source lives in `gpse/src/search-results/`. Compiled to `gpse/build/` via `@wordpress/scripts` (webpack). Never edit `gpse/build/` directly.
+
+**Tests**:
+- PHP: `tests/php/` — PHPUnit 9.6, bootstrap in `tests/bootstrap.php`
+- JS: `gpse/src/search-results/index.test.js` — Jest
+
+**Release artifact**: `dist/` directory produced by `make build`. PHP 8.2+ required.