feat #58 : wizard multi-étapes création/édition d'article

Remplace le formulaire unique par un wizard 5 étapes (création) et
6 étapes (édition) avec auto-sauvegarde en brouillon, détection de
tags depuis le texte (TagSuggester), aperçu SEO, diff avant validation
et plan Markdown dynamique dans l'éditeur.

Détail des changements :
- ArticleManager : +6 méthodes (updatePartialMeta, saveDraftOverlay,
  getDraftOverlay, hasDraftOverlay, discardDraftOverlay, commitDraftOverlay)
- .htaccess : routes /new/{uuid}/{1-5} et /edit/{uuid}/{1-6}
- index.php : cases create et edit réécrits en switch($step),
  nouveau case autosave_draft et edit_discard_draft
- assets/js/wizard.js : autosave debounce, auto-resize textarea,
  scroll curseur, plan TOC dynamique, toggle pills tags
- templates/wizard/ : nav.php + step1..6.php

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

src/ArticleManager.php

@@ -228,6 +228,126 @@ class ArticleManager
         return true;
     }
 
+    public function updatePartialMeta(string $uuid, array $updates): void
+    {
+        if (!$this->isValidUuid($uuid)) {
+            return;
+        }
+        $dir = $this->dataDir . '/' . $uuid;
+        $raw = @file_get_contents($dir . '/meta.json');
+        if ($raw === false) {
+            return;
+        }
+        $meta = json_decode($raw, true);
+        if (!is_array($meta)) {
+            return;
+        }
+        foreach ($updates as $key => $value) {
+            $meta[$key] = $value;
+        }
+        $meta['updated_at'] = date('Y-m-d H:i:s');
+        $this->writeMeta($dir, $meta);
+    }
+
+    public function saveDraftOverlay(string $uuid, array $metaFields, ?string $content = null): void
+    {
+        if (!$this->isValidUuid($uuid)) {
+            return;
+        }
+        $dir = $this->dataDir . '/' . $uuid;
+        $existing = [];
+        $raw = @file_get_contents($dir . '/draft_overlay.json');
+        if ($raw !== false) {
+            $existing = json_decode($raw, true) ?? [];
+        }
+        $overlay = array_merge($existing, $metaFields);
+        $overlay['_updated_at'] = date('Y-m-d H:i:s');
+        file_put_contents(
+            $dir . '/draft_overlay.json',
+            json_encode($overlay, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES) . "\n"
+        );
+        if ($content !== null) {
+            file_put_contents($dir . '/draft_overlay.md', $content);
+        }
+    }
+
+    public function getDraftOverlay(string $uuid): ?array
+    {
+        if (!$this->isValidUuid($uuid)) {
+            return null;
+        }
+        $dir = $this->dataDir . '/' . $uuid;
+        if (!file_exists($dir . '/draft_overlay.json')) {
+            return null;
+        }
+        $article = $this->getByUuid($uuid);
+        if (!$article) {
+            return null;
+        }
+        $raw = file_get_contents($dir . '/draft_overlay.json');
+        if ($raw === false) {
+            return null;
+        }
+        $overlay = json_decode($raw, true);
+        if (!is_array($overlay)) {
+            return null;
+        }
+        $merged = $article;
+        foreach ($overlay as $key => $value) {
+            if (!str_starts_with($key, '_')) {
+                $merged[$key] = $value;
+            }
+        }
+        if (file_exists($dir . '/draft_overlay.md')) {
+            $c = file_get_contents($dir . '/draft_overlay.md');
+            if ($c !== false) {
+                $merged['content'] = $c;
+            }
+        }
+        return $merged;
+    }
+
+    public function hasDraftOverlay(string $uuid): bool
+    {
+        if (!$this->isValidUuid($uuid)) {
+            return false;
+        }
+        return file_exists($this->dataDir . '/' . $uuid . '/draft_overlay.json');
+    }
+
+    public function discardDraftOverlay(string $uuid): void
+    {
+        if (!$this->isValidUuid($uuid)) {
+            return;
+        }
+        $dir = $this->dataDir . '/' . $uuid;
+        @unlink($dir . '/draft_overlay.json');
+        @unlink($dir . '/draft_overlay.md');
+    }
+
+    public function commitDraftOverlay(string $uuid, string $revisionComment = ''): void
+    {
+        $draft = $this->getDraftOverlay($uuid);
+        if (!$draft) {
+            return;
+        }
+        $this->update(
+            $uuid,
+            $draft['title'],
+            $draft['content'],
+            (bool)$draft['published'],
+            $draft['slug'] ?? '',
+            $draft['published_at'] ?? '',
+            $revisionComment,
+            $draft['seo_title'] ?? '',
+            $draft['seo_description'] ?? '',
+            $draft['og_image'] ?? '',
+            $draft['category'] ?? '',
+            $draft['tags'] ?? []
+        );
+        $this->discardDraftOverlay($uuid);
+    }
+
     public function addFileMeta(string $uuid, string $filename, string $author, string $sourceUrl, string $title = '', array $extraMeta = []): void
     {
         if (!$this->isValidUuid($uuid)) {