security: OWASP audit and hardening (v1.0.8)

- Archive XSS: wrap get_the_archive_title/description with wp_kses_post()
  in ContextBuilder to sanitize Editor-editable term content rendered via |raw
- Comment fields: esc_html() on comment_author, esc_url() on comment_author_url
  at data source; template updated to output pre-escaped URL via |raw
- dark-mode.js: whitelist localStorage value against ['dark','light'] to
  prevent attribute injection from third-party script tampering
- TwigService: add is_safe=>html to esc_html/esc_attr/esc_url Twig functions
  to prevent double-encoding if autoescape is ever enabled
- Add .markdownlint.json (disable MD024 duplicate headings, MD013 line length)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

inc/Template/ContextBuilder.php

@@ -245,8 +245,10 @@ class ContextBuilder
     private function getArchiveData(): array
     {
         return [
-            'title'       => get_the_archive_title(),
-            'description' => get_the_archive_description(),
+            // wp_kses_post() allows safe HTML (headings, links, spans) while stripping
+            // script/event-handler attributes that could be injected via term descriptions.
+            'title'       => wp_kses_post(get_the_archive_title()),
+            'description' => wp_kses_post(get_the_archive_description()),
         ];
     }
 
@@ -291,8 +293,10 @@ class ContextBuilder
 
             $tree[] = [
                 'id'         => (int) $comment->comment_ID,
-                'author'     => $comment->comment_author,
-                'author_url' => $comment->comment_author_url,
+                // Escape at source — comment_author is user-supplied, store as safe text.
+                'author'     => esc_html($comment->comment_author),
+                // esc_url() strips dangerous schemes (javascript:, data:) and encodes for HTML.
+                'author_url' => esc_url($comment->comment_author_url),
                 'avatar_url' => get_avatar_url($comment, ['size' => 40]),
                 'date'       => get_comment_date('', $comment),
                 'date_iso'   => get_comment_date('c', $comment),