Add PHPUnit test suite with 64 unit tests (v1.1.1)

PHPUnit 11 + Brain\Monkey for WordPress function mocking. Tests cover
BlockRenderer (28), WidgetRenderer (9), NavWalker (14), and
TemplateController (12). Includes functional WP_HTML_Tag_Processor stub,
CI test job between lint and build-release, prebuild hook gating npm
build on passing tests, and release package exclusions for test files.

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

package.json

@@ -33,6 +33,8 @@
         "copy:js": "copyfiles -f node_modules/bootstrap/dist/js/bootstrap.bundle.min.js node_modules/bootstrap/dist/js/bootstrap.bundle.min.js.map assets/js/",
         "copy:theme-js": "copyfiles -f src/js/dark-mode.js assets/js/",
         "copy:icons": "copyfiles -f node_modules/bootstrap-icons/font/fonts/bootstrap-icons.woff node_modules/bootstrap-icons/font/fonts/bootstrap-icons.woff2 assets/fonts/",
+        "test": "composer exec -- phpunit",
+        "prebuild": "npm run test",
         "build": "npm run copy:js && npm run copy:theme-js && npm run copy:icons && npm run scss && npm run scss:rtl && npm run postcss",
         "watch": "npm run copy:js && npm run scss:watch",
         "dev": "npm run watch"