feat(UI-Overhaul-Phase3): Wiki WYSIWYG Editor mit Tiptap

- WikiEditor.tsx: Complete rebuild with Tiptap WYSIWYG editor
  - Notion-style floating toolbar with bold/italic/underline/strike
  - Headings (H1/H2/H3), bullet/ordered lists, blockquote, code blocks
  - Link and image insertion
  - Text alignment (left/center/right)
  - Undo/redo support
  - HTML-to-Markdown conversion for backend storage
  - Markdown-to-HTML conversion for editor initialization
- Wiki.tsx: View/Edit mode toggle
  - View mode: Rendered Markdown (ReactMarkdown)
  - Edit mode: WYSIWYG editor (Tiptap)
  - Inline save button in edit mode
  - wikiMode resets to view when selecting new article
  - handleInlineSave saves article content directly

tsc clean

frontend/src/pages/Wiki.tsx

@@ -81,6 +81,7 @@ export function WikiPage() {
   const [deleting, setDeleting] = useState(false);
   const [restoring, setRestoring] = useState(false);
   const [browserRefreshKey, setBrowserRefreshKey] = useState(0);
+  const [wikiMode, setWikiMode] = useState<'view' | 'edit'>('view');
 
   const loadCategories = useCallback(async () => {
     try {
@@ -112,6 +113,7 @@ export function WikiPage() {
   const handleSelectArticle = useCallback(
     (a: WikiArticle) => {
       void loadArticle(a.id);
+      setWikiMode('view');
     },
     [loadArticle]
   );
@@ -172,6 +174,30 @@ export function WikiPage() {
     }
   }, [form, editingId, t, toast]);
 
+  // Inline save from View/Edit mode toggle
+  const handleInlineSave = useCallback(async () => {
+    if (!article) return;
+    setSaving(true);
+    try {
+      const updated = await updateWikiArticle(article.id, {
+        title: article.title,
+        content: article.content,
+        summary: article.summary,
+        category_id: article.category_id,
+        tags: article.tags,
+        status: article.status,
+      });
+      setArticle(updated);
+      toast.success(t('knowledge.editor.updated'));
+      setWikiMode('view');
+      setBrowserRefreshKey((k) => k + 1);
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : t('knowledge.editor.saveError'));
+    } finally {
+      setSaving(false);
+    }
+  }, [article, t, toast]);
+
   const handleDelete = useCallback(async () => {
     if (!deleteTarget) return;
     setDeleting(true);
@@ -255,12 +281,22 @@ export function WikiPage() {
               actions={
                 <div className="flex items-center gap-2">
                   {statusBadge}
+                  <Button
+                    variant="ghost"
+                    size="sm"
+                    onClick={() => setWikiMode(wikiMode === 'view' ? 'edit' : 'view')}
+                    icon={wikiMode === 'view' ? <Pencil className="h-4 w-4" aria-hidden="true" /> : <History className="h-4 w-4" aria-hidden="true" />}
+                  >
+                    {wikiMode === 'view' ? t('common.edit') : t('common.preview', 'Vorschau')}
+                  </Button>
+                  {wikiMode === 'edit' && (
+                    <Button variant="ghost" size="sm" onClick={() => void handleInlineSave()} isLoading={saving}>
+                      {t('common.save')}
+                    </Button>
+                  )}
                   <Button variant="ghost" size="sm" onClick={() => void loadVersions()} icon={<History className="h-4 w-4" aria-hidden="true" />}>
                     {t('knowledge.versions.title')}
                   </Button>
-                  <Button variant="ghost" size="sm" onClick={openEdit} icon={<Pencil className="h-4 w-4" aria-hidden="true" />}>
-                    {t('common.edit')}
-                  </Button>
                   <Button variant="danger" size="sm" onClick={() => setDeleteTarget(article)} icon={<Trash2 className="h-4 w-4" aria-hidden="true" />}>
                     {t('common.delete')}
                   </Button>
@@ -308,9 +344,19 @@ export function WikiPage() {
                 </div>
               )}
 
-              <div className="prose prose-sm max-w-none">
-                <ReactMarkdown remarkPlugins={[remarkGfm]}>{article.content || t('wiki.detail.emptyContent')}</ReactMarkdown>
-              </div>
+              {wikiMode === 'edit' ? (
+                <div>
+                  <WikiEditor
+                    value={article.content}
+                    onChange={(value) => setArticle({ ...article, content: value })}
+                    placeholder={t('wiki.editor.contentPlaceholder')}
+                  />
+                </div>
+              ) : (
+                <div className="prose prose-sm max-w-none">
+                  <ReactMarkdown remarkPlugins={[remarkGfm]}>{article.content || t('wiki.detail.emptyContent')}</ReactMarkdown>
+                </div>
+              )}
             </Card>
           ) : (
             <EmptyState