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/WarningsTest.php

@@ -7,7 +7,8 @@ namespace LIT\MCP\Tests\Unit\Integrations\Divi\Compose;
 use LIT\MCP\Integrations\Divi\BlockTree\Document;
 use LIT\MCP\Integrations\Divi\BlockTree\NodeIndex;
 use LIT\MCP\Integrations\Divi\Compose\Warnings;
-use LIT\MCP\Tests\Unit\Integrations\Divi\Design\DesignSystemTest;
+use LIT\MCP\Tests\Support\ComposeFixture;
+use LIT\MCP\Tests\Support\DiviFixtures;
 use PHPUnit\Framework\TestCase;
 
 final class WarningsTest extends TestCase
@@ -34,7 +35,7 @@ final class WarningsTest extends TestCase
             $document->append($block);
         }
 
-        $warnings = (new Warnings(DesignSystemTest::sample()))->collect(NodeIndex::build($document), $composed['blocks']);
+        $warnings = (new Warnings(DiviFixtures::designSystem()))->collect(NodeIndex::build($document), $composed['blocks']);
 
         self::assertSame(
             [
@@ -50,6 +51,6 @@ final class WarningsTest extends TestCase
             $warnings
         );
 
-        self::assertSame([], (new Warnings(DesignSystemTest::sample()))->collect(NodeIndex::build($document), []));
+        self::assertSame([], (new Warnings(DiviFixtures::designSystem()))->collect(NodeIndex::build($document), []));
     }
 }