perf : getAll() sans contenu, search_index + featured, excerpts via plain (v1.6.14)

- loadArticle($dir, false) dans loadAll() — meta.json seulement, pas d'index.md
- loadAll() enrichit les articles avec plain depuis search_index (1 lecture JSON)
- rebuildSearchIndex() lit index.md directement + ajoute featured au schéma
- getSearchIndex() rebuilde automatiquement si featured absent
- post_list, author_articles, author_profile : excerpts via plain, plus de Parsedown
- Ferme #24

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

templates/author_profile.php

@@ -1,6 +1,4 @@
 <?php
-require_once BASE_PATH . '/src/Parsedown.php';
-$Parsedown = new Parsedown();
 
 ob_start();
 
@@ -36,8 +34,7 @@ $_initials = mb_strtoupper(mb_substr($_apName, 0, 1, 'UTF-8'), 'UTF-8');
 <?php else: ?>
     <div class="post-grid">
     <?php foreach (array_slice($authorArticles, 0, 6) as $post):
-        $html     = $Parsedown->text($post['content']);
-        $preview  = mb_strimwidth(strip_tags($html), 0, 120, '…');
+        $preview  = mb_strimwidth($post['plain'] ?? '', 0, 120, '…');
         $category = trim((string)($post['category'] ?? ''));
         $gradient = coverGradient($category !== '' ? $category : $post['uuid'], $allCats ?? []);
         $postUrl  = '/post/' . rawurlencode($post['slug']);