fix: bound render-summary strings, restore postdata globals, drain buffers

Review fix round 1 for lit/page-render-summary: extract shared Text::shorten()
(reused by NodeSummary), replace data: URIs with a short marker, prefer
data-src/data-lazy-src over placeholder src, dedup nested p/li/blockquote
text and ignore script/style/noscript content, restore every setup_postdata
global (not just $post), drain output buffers robustly around the_content,
and disclose that rendering can trigger oEmbed/network requests.

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

src/Integrations/Divi/BlockTree/NodeSummary.php

@@ -4,6 +4,8 @@ declare(strict_types=1);
 
 namespace LIT\MCP\Integrations\Divi\BlockTree;
 
+use LIT\MCP\Abilities\Text;
+
 /**
  * Short human-readable facts about a node for the outline: admin label, first text,
  * preset IDs, column layout. Pure PHP.
@@ -36,7 +38,7 @@ final class NodeSummary
         foreach ($paths as $path) {
             $text = self::textOf(AttrMap::desktop($block->attrs(), $path));
             if ($text !== '') {
-                return self::shorten($text, $max);
+                return Text::shorten($text, $max);
             }
         }
 
@@ -130,9 +132,4 @@ final class NodeSummary
 
         return $index === false ? count(self::PRIORITY) : (int) $index;
     }
-
-    private static function shorten(string $text, int $max): string
-    {
-        return mb_strlen($text) > $max ? rtrim(mb_substr($text, 0, $max - 1)) . '…' : $text;
-    }
 }