Phase 4 cleanup: migrate old tests to PHPUnit, add ErrorHandler/PureLogic/SearchController tests, remove app/tests/, update justfile test target

justfile

@@ -339,10 +339,13 @@ deploy-all-first: deploy deploy-backup
 
 [group('test')]
 test:
-    # Run all tests. To run a subset, use:
-    #   php app/tests/Unit/DatabaseTest.php
-    #   php app/tests/Integration/SearchTest.php
-    @php app/tests/run-tests.php
+    # Run all PHPUnit tests
+    @vendor/bin/phpunit tests/phpunit/
+
+[group('test')]
+test-coverage:
+    # Generate HTML coverage report in coverage/
+    @vendor/bin/phpunit --coverage-html coverage/ tests/phpunit/
 
 [group('test')]
 lint-biome: