feat: add php rule pack

rules/php/testing.md

@@ -0,0 +1,34 @@
+---
+paths:
+  - "**/*.php"
+  - "**/phpunit.xml"
+  - "**/phpunit.xml.dist"
+  - "**/composer.json"
+---
+# PHP Testing
+
+> This file extends [common/testing.md](../common/testing.md) with PHP specific content.
+
+## Framework
+
+Use **PHPUnit** as the default test framework. **Pest** is also acceptable when the project already uses it.
+
+## Coverage
+
+```bash
+vendor/bin/phpunit --coverage-text
+# or
+vendor/bin/pest --coverage
+```
+
+Prefer **pcov** or **Xdebug** in CI, and keep coverage thresholds in CI rather than as tribal knowledge.
+
+## Test Organization
+
+- Separate fast unit tests from framework/database integration tests.
+- Use factory/builders for fixtures instead of large hand-written arrays.
+- Keep HTTP/controller tests focused on transport and validation; move business rules into service-level tests.
+
+## Reference
+
+See skill: `tdd-workflow` for the repo-wide RED -> GREEN -> REFACTOR loop.