fix: full-form internal links follow the {{link:}} target rules (ruling P10)

One PostIdParser for {{link:}} and select_post; post_link_url_<type> needs a
living, readable, non-attachment target of exactly that type.

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

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

@@ -415,6 +415,11 @@ final class StoredNodeGuardTest extends TestCase
             {
                 return $this->inner->canReadPost($id);
             }
+
+            public function linkTargetType(int $id): ?string
+            {
+                return $this->inner->linkTargetType($id);
+            }
         };
         $references = new VariableRef(
             DiviFixtures::designSystem(),