feat: show category icon when no channel selected

Add a disabled category icon button next to the "Select category"
placeholder in the live stream layout when no channel is selected, and
align the placeholder text and icon with flex and spacing. This gives a
clearer visual cue for the missing category.

Also add missing translation keys ("SELECT_CATEGORY" and "PAGE") to
English, Russian and German locale files so the new UI text and paging
label are available across supported languages.

apps/web/src/app/xtream-tauri/live-stream-layout/live-stream-layout.component.html

@@ -40,6 +40,9 @@
         </div>
     } @else {
         <div class="no-channel-selected">
+            <button mat-icon-button disabled>
+                <mat-icon>category</mat-icon>
+            </button>
             {{ 'PORTALS.SELECT_CATEGORY' | translate }}
         </div>
     }

apps/web/src/app/xtream-tauri/live-stream-layout/live-stream-layout.component.scss

@@ -53,6 +53,9 @@
     margin: 0;
     font-size: 1.2rem;
     font-weight: 500;
+    display: flex;
+    align-items: center;
+    gap: 10px;
 }
 
 ::ng-deep {