Initial implementation of WooCommerce Composable Products plugin

Implemented custom WooCommerce product type allowing customers to build their own
product bundles by selecting from predefined sets of products.

Features:
- Custom "Composable Product" type with admin interface
- Product selection by category, tag, or SKU
- Configurable selection limits (global and per-product)
- Dual pricing modes: fixed price or sum of selected products
- Modern responsive frontend with Twig templates
- AJAX add-to-cart functionality
- Full internationalization support (.pot file)
- WooCommerce settings integration
- Comprehensive documentation

Technical implementation:
- PHP 8.3+ with PSR-4 autoloading
- Twig 3.0 templating engine via Composer
- Vanilla JavaScript with jQuery for frontend interactions
- WordPress and WooCommerce hooks for seamless integration
- Security: input sanitization, validation, and output escaping
- Translation-ready with text domain 'wc-composable-product'

Documentation:
- README.md: Project overview and features
- INSTALL.md: Installation and usage guide
- IMPLEMENTATION.md: Technical architecture
- CHANGELOG.md: Version history

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

assets/css/admin.css

@@ -0,0 +1,43 @@
+/**
+ * Admin Styles for Composable Products
+ *
+ * @package WC_Composable_Product
+ */
+
+#composable_product_data {
+    padding: 12px;
+}
+
+.composable_criteria_group {
+    border-top: 1px solid #eee;
+    padding-top: 12px;
+    margin-top: 12px;
+}
+
+#_composable_categories,
+#_composable_tags {
+    min-height: 150px;
+}
+
+.show_if_composable {
+    display: none;
+}
+
+.product-type-composable .show_if_composable {
+    display: block;
+}
+
+.composable_options.composable_tab a::before {
+    content: '\f323';
+    font-family: 'Dashicons';
+}
+
+/* Enhanced select styling */
+.wc-composable-product-admin .select2-container {
+    min-width: 50%;
+}
+
+/* Help tips */
+.woocommerce-help-tip {
+    color: #666;
+}