fix: resolve horizontal layout blowout in mobile dashboard list view

src/NexusReader.UI.Shared/Components/Organisms/CurrentReadingWidget.razor

@@ -7,7 +7,7 @@
     {
         <div @key='"current-reading-book"' class="card-layout">
             <div class="book-cover">
-                <img src="@(Book.CoverUrl ?? "https://via.placeholder.com/120x180?text=No+Cover")" alt="@Book.Title" />
+                <img src="@(string.IsNullOrEmpty(Book.CoverUrl) ? "https://via.placeholder.com/120x180?text=No+Cover" : Book.CoverUrl)" alt="@Book.Title" />
             </div>
             
             <div class="book-details">
@@ -42,7 +42,7 @@
 
                 <div class="actions">
                     <button class="btn-nexus outline" @onclick="HandleContinueReading">
-                        Continue Reading
+                        Kontynuuj czytanie
                         <NexusIcon Name="arrow-right" Size="16" />
                     </button>
                 </div>