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>

composer.json

@@ -14,11 +14,20 @@
         "php": ">=8.3",
         "twig/twig": "^3.0"
     },
+    "require-dev": {
+        "brain/monkey": "^2.6",
+        "phpunit/phpunit": "^11.0"
+    },
     "autoload": {
         "psr-4": {
             "WPBootstrap\\": "inc/"
         }
     },
+    "autoload-dev": {
+        "psr-4": {
+            "WPBootstrap\\Tests\\": "tests/"
+        }
+    },
     "config": {
         "optimize-autoloader": true,
         "sort-packages": true