fix(admin): show error toast instead of success when savePost fails

api() returns null on HTTP error; the save block now checks the return
value before closing the modal and showing the success toast.

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

DrSousan.Api/wwwroot/admin/index.html

@@ -2103,8 +2103,10 @@ async function savePost(){
     categoryId:catId?parseInt(catId):null,
     ogImage:document.getElementById('post-image').value,
   };
-  if(id) await api(`/api/blog/posts/${id}`,{method:'PUT',body:JSON.stringify(body)});
-  else   await api('/api/blog/posts',{method:'POST',body:JSON.stringify(body)});
+  const res = id
+    ? await api(`/api/blog/posts/${id}`,{method:'PUT',body:JSON.stringify(body)})
+    : await api('/api/blog/posts',{method:'POST',body:JSON.stringify(body)});
+  if(res === null && id) return; // api() already showed error toast
   closeModal('postModal'); toast('مقاله ذخیره شد ✓'); loadPosts();
 }