Feat: pages Article + navigation blog/article interne

- Router: findSlideIndex() avec fallback parent path
  (/blog/slug → /blog) pour sub-pages
- article.json.php: réécriture — date, intro, cover, body (blocks→HTML),
  related articles (fallback siblings si vide)
- Article.svelte: sous-composant — topbar date+retour, titre Terminal,
  intro, cover, body rich text (styles :global pour blocks Kirby),
  related articles grid, responsive
- Blog.svelte: gère deux modes (liste + article) —
  intercepte les clics article via stopPropagation (avant le router),
  fetch article data, pushState pour URL, popstate pour back/forward,
  direct navigation /blog/slug sur mount

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

site/templates/article.json.php

@@ -6,26 +6,19 @@ if ($related->isEmpty()) {
 }
 
 $specificData = [
-  'date' => $page->date()->toDate('Y-m-d'),
-  'dateFormatted' => $page->date()->toDate('d/m/Y'),
-  'intro' => $page->intro()->value(),
-  'author' => [
-    'name' => $page->authorName()->value(),
-    'role' => $page->authorRole()->value(),
-    'photo' => $page->authorPhoto()->toFile()?->url()
-  ],
-  'cover' => $page->cover()->toFile()?->url(),
-  'content' => $page->articleContent()->toBlocks(),
-  'tags' => $page->tags()->split(),
-  'related' => $related->map(function($rec) {
+  'date'      => $page->date()->toDate('d/m/Y'),
+  'intro'     => $page->intro()->value(),
+  'cover'     => $page->cover()->toFile()?->url(),
+  'body'      => (string) $page->body()->toBlocks(),
+  'related'   => $related->map(function($rec) {
     return [
       'title' => $rec->title()->value(),
-      'url' => $rec->url(),
-      'category' => $rec->category()->value(),
-      'cover' => $rec->cover()->toFile()?->thumb(['width' => 400])->url()
+      'slug'  => $rec->slug(),
+      'date'  => $rec->date()->toDate('d/m/Y'),
+      'cover' => $rec->cover()->toFile()?->url(),
     ];
   })->values(),
-  'parentUrl' => $page->parent()->url()
+  'parentUrl' => $page->parent()->url(),
 ];
 
 $pageData = array_merge($genericData, $specificData);