docs: add copilot instructions for bluem-woocommerce plugin

This commit introduces a new documentation file outlining the project overview, repository layout, key commands, coding conventions, and release workflow for the bluem-woocommerce plugin. This will assist developers in understanding the structure and usage of the plugin more effectively.

Author: daanrijpkemacb

.github/copilot-instructions.md

@@ -0,0 +1,58 @@
+# Copilot Instructions — bluem-woocommerce
+
+## Project overview
+
+WordPress + WooCommerce plugin providing Bluem payment, eMandates and iDIN identity services.  
+PHP 8.0+, using the `bluem-development/bluem-php` SDK. Licensed GPL v3.
+
+## Repository layout
+
+| Path | Purpose |
+|---|---|
+| `bluem.php` | Main plugin entry point (WP plugin header) |
+| `bluem-*.php` | Feature modules (payments, mandates, iDIN, login, etc.) |
+| `gateways/` | WooCommerce payment gateway classes |
+| `src/` | Namespaced PHP classes (`Bluem\Wordpress\…`) |
+| `views/` | Admin page templates |
+| `css/`, `js/` | Front-end assets |
+| `tests/Unit/`, `tests/Acceptance/` | PHPUnit + Codeception tests |
+| `docker-compose.yml` | Local dev env (MySQL 5.7, WordPress, phpMyAdmin) |
+| `svn-directory/` | WordPress.org SVN checkout for plugin releases |
+| `build/` | Generated build output (do **not** edit directly) |
+| `Makefile` | Dev & release tasks (see below) |
+
+## Key commands
+
+```sh
+make install            # composer install
+make unit_test          # PHPUnit
+make acceptance_test    # Codeception
+make lint               # php-cs-fixer check
+make lint_fix           # php-cs-fixer fix
+make copy-to-docker     # build & copy plugin into Docker env
+make prepare-release NEW_TAG=x.y.z   # build, tag, update trunk (SVN)
+make release            # commit prepared release to WP SVN
+```
+
+## Coding conventions
+
+- `declare(strict_types=1);` in all PHP files.
+- Follow WordPress Coding Standards (WPCS) and PSR-12 where compatible.
+- Use typed properties, return types, union types, readonly, enums (PHP 8.x).
+- WordPress globals and hooks: use `add_action` / `add_filter`; avoid direct DB queries — use `$wpdb` with prepared statements.
+- WooCommerce gateway classes extend `WC_Payment_Gateway`.
+- Escape all output (`esc_html`, `esc_attr`, `wp_kses_post`). Sanitise all input (`sanitize_text_field`, `absint`, etc.).
+
+## Release workflow
+
+1. Bump version in `bluem.php` plugin header and `build.env`.
+2. `make prepare-release NEW_TAG=x.y.z` — builds into `build/`, copies to `svn-directory/tags/` and `svn-directory/trunk/`.
+3. `make release` — commits tag + trunk to WordPress.org SVN.
+
+## Things to watch out for
+
+- `build/` and `svn-directory/` are deployment artifacts; never edit them directly.
+- Docker volumes live under `docker/`; plugin code is mounted via `docker/plugins/`.
+- The plugin depends on `bluem-development/bluem-php` — check its API when suggesting SDK calls.
+- Keep WP compatibility ≥ 5.0 and WC compatibility reasonable.
+