Add PHPUnit test suite, PSR-4 refactor, lint+test CI jobs (v1.3.1)

- 57 unit tests covering ProductType, StockManager, CartHandler, Plugin,
  Admin/ProductData, Admin/Settings using Brain Monkey + Mockery
- WooCommerce class stubs for testing without WP installation
- PHP lint and test jobs in release workflow (test gate blocks release)
- PSR-4 namespace change: WC_Composable_Product -> Magdev\WcComposableProduct
- PascalCase filenames for all classes under includes/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/stubs/class-wc-admin-settings.php

@@ -0,0 +1,11 @@
+<?php
+/**
+ * Minimal WC_Admin_Settings stub for unit testing.
+ */
+class WC_Admin_Settings {
+    public static function output_fields($options) {
+    }
+
+    public static function save_fields($options) {
+    }
+}

tests/stubs/class-wc-cart.php

@@ -0,0 +1,15 @@
+<?php
+/**
+ * Minimal WC_Cart stub for unit testing.
+ */
+class WC_Cart {
+    protected $cart_contents = [];
+
+    public function get_cart() {
+        return $this->cart_contents;
+    }
+
+    public function set_cart_contents($contents) {
+        $this->cart_contents = $contents;
+    }
+}

tests/stubs/class-wc-data.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * Minimal WC_Data stub for unit testing.
+ */
+class WC_Data {
+    protected $id = 0;
+    protected $data = [];
+    protected $meta_data = [];
+
+    public function __construct($id = 0) {
+        if (is_numeric($id) && $id > 0) {
+            $this->id = (int) $id;
+        }
+    }
+
+    public function get_id() {
+        return $this->id;
+    }
+
+    public function set_id($id) {
+        $this->id = (int) $id;
+    }
+
+    public function get_meta($key, $single = true, $context = 'view') {
+        return $this->meta_data[$key] ?? ($single ? '' : []);
+    }
+
+    public function update_meta_data($key, $value, $meta_id = 0) {
+        $this->meta_data[$key] = $value;
+    }
+
+    public function save() {
+        return $this->get_id();
+    }
+}

tests/stubs/class-wc-order-item-product.php

@@ -0,0 +1,28 @@
+<?php
+/**
+ * Minimal WC_Order_Item_Product stub for unit testing.
+ */
+class WC_Order_Item_Product extends WC_Data {
+    protected $product = null;
+    protected $quantity = 1;
+
+    public function get_product() {
+        return $this->product;
+    }
+
+    public function set_product($product) {
+        $this->product = $product;
+    }
+
+    public function get_quantity() {
+        return $this->quantity;
+    }
+
+    public function set_quantity($quantity) {
+        $this->quantity = $quantity;
+    }
+
+    public function add_meta_data($key, $value, $unique = false) {
+        $this->meta_data[$key] = $value;
+    }
+}

tests/stubs/class-wc-order.php

@@ -0,0 +1,24 @@
+<?php
+/**
+ * Minimal WC_Order stub for unit testing.
+ */
+class WC_Order extends WC_Data {
+    protected $items = [];
+    protected $order_notes = [];
+
+    public function get_items($type = '') {
+        return $this->items;
+    }
+
+    public function set_items($items) {
+        $this->items = $items;
+    }
+
+    public function add_order_note($note) {
+        $this->order_notes[] = $note;
+    }
+
+    public function get_order_notes() {
+        return $this->order_notes;
+    }
+}

tests/stubs/class-wc-product.php

@@ -0,0 +1,88 @@
+<?php
+/**
+ * Minimal WC_Product stub for unit testing.
+ */
+class WC_Product extends WC_Data {
+    protected $supports = [];
+    protected $data = [
+        'name' => '',
+        'price' => '',
+        'regular_price' => '',
+        'status' => 'publish',
+    ];
+
+    public function get_type() {
+        return 'simple';
+    }
+
+    public function get_name($context = 'view') {
+        return $this->data['name'] ?? '';
+    }
+
+    public function get_price($context = 'view') {
+        return $this->data['price'] ?? '';
+    }
+
+    public function get_regular_price($context = 'view') {
+        return $this->data['regular_price'] ?? '';
+    }
+
+    public function get_price_html() {
+        return '';
+    }
+
+    public function get_permalink() {
+        return '';
+    }
+
+    public function get_image_id($context = 'view') {
+        return 0;
+    }
+
+    public function get_stock_quantity($context = 'view') {
+        return null;
+    }
+
+    public function get_stock_status($context = 'view') {
+        return 'instock';
+    }
+
+    public function get_children() {
+        return [];
+    }
+
+    public function is_type($type) {
+        return $this->get_type() === $type;
+    }
+
+    public function is_purchasable() {
+        return true;
+    }
+
+    public function is_in_stock() {
+        return true;
+    }
+
+    public function managing_stock() {
+        return false;
+    }
+
+    public function backorders_allowed() {
+        return false;
+    }
+
+    public function is_sold_individually() {
+        return false;
+    }
+
+    public function set_price($price) {
+        $this->data['price'] = $price;
+    }
+
+    public function set_stock_quantity($quantity) {
+    }
+
+    public function supports($feature) {
+        return in_array($feature, $this->supports, true);
+    }
+}

tests/stubs/class-wc-settings-page.php

@@ -0,0 +1,29 @@
+<?php
+/**
+ * Minimal WC_Settings_Page stub for unit testing.
+ */
+class WC_Settings_Page {
+    protected $id = '';
+    protected $label = '';
+
+    public function __construct() {
+    }
+
+    public function get_id() {
+        return $this->id;
+    }
+
+    public function get_label() {
+        return $this->label;
+    }
+
+    public function get_settings() {
+        return [];
+    }
+
+    public function output() {
+    }
+
+    public function save() {
+    }
+}