fix: stop guessing a kind for composite Divi attribute paths

Review fix round 1 on the lit/divi-catalog task:
- AttrPathIndex::collectKinds() no longer records a kind from a
  component.type === "group" node (a composite of several sub-kinds,
  e.g. button.innerContent = text + link + target), and kinds() now
  drops any attrName with more than one distinct candidate kind
  instead of last-write-wins (e.g. imageIcon.innerContent had onoff +
  icon + image sub-fields sharing one attrName). Both previously
  produced a wrong-but-present kind, which is more dangerous for 2b's
  sanitization routing than "unknown". Verified against the committed
  blurb/button/fullwidth-header fixture entries and live against the
  full 100-module catalog.
- AttrPathIndex::fromDefaults() now builds on AttrMap::flatten()
  instead of a parallel walker.
- ModuleCatalog::shortName() replaces the duplicated
  substr($name, strlen('divi/')) in DiviCatalogAbility.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

tests/Unit/Integrations/Divi/Schema/DiviCatalogAbilityTest.php

@@ -54,8 +54,10 @@ final class DiviCatalogAbilityTest extends TestCase
     {
         $button = $this->ability()->execute(['module' => 'divi/button'])['module'];
 
-        self::assertSame('url', $button['path_kinds']['button.innerContent']);
+        self::assertSame('text', $button['path_kinds']['module.meta.adminLabel']);
         self::assertArrayNotHasKey('no.such.path', $button['path_kinds']);
+        // Composite ("group") paths are left out rather than guessing a single kind.
+        self::assertArrayNotHasKey('button.innerContent', $button['path_kinds']);
     }
 
     public function testUnknownModuleAndPermission(): void