test: shared Divi fixtures in tests/Support (T1)

- DiviFixtures: markup(), givenPost(), schema(), designSystem(), catalog(),
  dynamicContentRegistry(), maliciousRefs() - moved verbatim out of
  DiviPageLoaderTest, DesignSystemTest, ModuleCatalogTest, DynamicContentMapTest
  and VariableRefTest (its malicious() provider now returns maliciousRefs()).
- ComposeFixture moves to tests/Support.
- DiviWriterFixture: modules(), designReader(), composition(), a recording saver(),
  log() and writer(&$saved, &$failures, unfiltered, loader) for the five tests that
  wired the Divi write stack by hand.
No test cases or assertions changed (1397 / 5834).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/Unit/Integrations/Divi/Compose/ComposerTest.php

@@ -11,8 +11,8 @@ use LIT\MCP\Integrations\Divi\BlockTree\Parser;
 use LIT\MCP\Integrations\Divi\BlockTree\Serializer;
 use LIT\MCP\Integrations\Divi\Compose\Composer;
 use LIT\MCP\Integrations\Divi\Design\DesignSystem;
-use LIT\MCP\Tests\Unit\Integrations\Divi\Design\DesignSystemTest;
-use LIT\MCP\Tests\Unit\Integrations\Divi\Schema\ModuleCatalogTest;
+use LIT\MCP\Tests\Support\ComposeFixture;
+use LIT\MCP\Tests\Support\DiviFixtures;
 use PHPUnit\Framework\TestCase;
 
 final class ComposerTest extends TestCase
@@ -442,11 +442,11 @@ final class ComposerTest extends TestCase
         $this->expectException(InvalidArgumentException::class);
 
         new Composer(
-            ModuleCatalogTest::sampleCatalog(),
+            DiviFixtures::catalog(),
             ComposeFixture::rules(),
             ComposeFixture::shortform(),
             ComposeFixture::attrWriter(),
-            DesignSystemTest::sample(),
+            DiviFixtures::designSystem(),
             '5.2.1"},"x":{"'
         );
     }