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/Abilities/Text.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Abilities;
+
+/**
+ * Small text helper shared by every summary that must stay bounded in size (outlines, node
+ * summaries, the rendered-page excerpt): extracts are a fixed-size preview, never an unbounded
+ * copy of user/plugin content. Pure PHP.
+ */
+final class Text
+{
+    /** Shortens to at most $max characters (multi-byte aware), appending an ellipsis. */
+    public static function shorten(string $text, int $max): string
+    {
+        return mb_strlen($text) > $max ? rtrim(mb_substr($text, 0, $max - 1)) . '…' : $text;
+    }
+}