test: add PHPUnit 11.5 unit test suite

- phpunit.xml.dist with unit suite and source coverage config
- .phpunit.cache excluded in .gitignore
- Initial SvgRendererTest as example test
- .claude/settings.json with PostToolUse hook to auto-run phpunit on edit

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

.gitignore

@@ -4,3 +4,4 @@
 /var/
 /public/bundles/
 composer.lock
+/.phpunit.cache