feat: hide tool list and instructions from users without LIT MCP access

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

src/Plugin.php

@@ -20,6 +20,7 @@ use LIT\MCP\Integrations\WordPress\Schema\SampledMetaSource;
 use LIT\MCP\Integrations\WordPress\WordPressIntegration;
 use LIT\MCP\Server\RequestContext;
 use LIT\MCP\Server\ServerRegistrar;
+use LIT\MCP\Server\VisibilityFilter;
 
 /**
  * Wires WP-LIT-MCP into WordPress.
@@ -42,6 +43,7 @@ final class Plugin
 
         (new Access())->register();
         (new RequestContext())->register();
+        (new VisibilityFilter())->register();
 
         $limits = new Limits();
         $changeLog = new ChangeLog();