Add PHPUnit test suite with Brain\Monkey (v0.1.6)

Add test infrastructure for isolated unit testing without WordPress/WooCommerce:
- 27 tests (54 assertions) covering TemplateOverride and WooCommerceExtension
- Brain\Monkey for WordPress function mocking, class stubs for TwigService and WC_Product
- PHPUnit test job added to Gitea CI pipeline between lint and build-release
- Test artifacts excluded from release packages

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

README.md

@@ -28,8 +28,9 @@ The bridge hooks into WooCommerce's `woocommerce_before_template_part` and `wooc
 
 - **99 Twig template overrides** covering all customer-facing WooCommerce pages
 - **Rendering bridge** (`WooCommerceExtension` + `TemplateOverride`) that intercepts WooCommerce's PHP template pipeline
-- **~50 Twig functions** and **7 Twig filters** exposing WooCommerce and WordPress APIs to templates
+- **~50 Twig functions** and **8 Twig filters** exposing WooCommerce and WordPress APIs to templates
 - Bootstrap 5 responsive markup with dark mode support
+- **PHPUnit test suite** with Brain\Monkey for isolated unit testing (no WordPress/WooCommerce required)
 - HPOS compatible (uses `WC_Order` methods only, no `$post` global)
 - 8 reusable Twig components (card, pagination, price, rating, address-card, status-badge, quantity-input, form-field)
 - Translation-ready
@@ -83,10 +84,15 @@ wc-bootstrap/
 │   ├── notices/
 │   ├── order/
 │   └── single-product/
+├── tests/
+│   ├── bootstrap.php          # PHPUnit bootstrap (autoloader + stubs)
+│   ├── Stubs/                 # WordPress/WooCommerce class stubs
+│   └── Unit/                  # Unit tests (TemplateOverride, WooCommerceExtension)
 ├── docker/
 │   ├── Dockerfile             # Multistage build (WC download, npm, composer, WP)
 │   ├── entrypoint.sh          # Auto-setup wrapper entrypoint
 │   └── setup.sh               # First-run WP install + plugin/theme activation
+├── phpunit.xml.dist           # PHPUnit 11 configuration
 ├── .env-dist                  # Environment variable template
 ├── compose.yaml               # WordPress + MariaDB services
 ├── compose.override.yaml      # Dev overrides (bind mounts, debug flags)
@@ -143,8 +149,8 @@ for po in languages/wc-bootstrap-*.po; do msgfmt -o "${po%.po}.mo" "$po"; done
 Releases are automated via Gitea Actions. Push a tag matching `vX.X.X` to trigger a release build.
 
 ```bash
-git tag -a v0.1.5 -m "Version 0.1.5 - Fix 10 known bugs"
-git push origin v0.1.5
+git tag -a v0.1.6 -m "Version 0.1.6 - Add PHPUnit test suite"
+git push origin v0.1.6
 ```
 
 ## License