refactor: 调整媒体库网格视图的滚动与布局结构

ui/src/app/library-browser.component.html

@@ -67,7 +67,8 @@
       </div>
     </div>
 
-    <div class="grid" *ngIf="view === 'grid'">
+    <div class="grid-wrap" *ngIf="view === 'grid'">
+      <div class="grid">
         <div class="card" *ngFor="let file of filteredFiles; trackBy: trackByName" [class.selected]="isSelected(filePath(file))">
           <input type="checkbox" class="card-check" [checked]="isSelected(filePath(file))" (change)="toggleSelect(filePath(file), $event.target.checked)" [attr.aria-label]="'选择 ' + file.name">
           <div class="thumb clickable" (click)="play.emit(file)">
@@ -94,6 +95,7 @@
         </div>
       </div>
     </div>
+  </div>
 
   <div class="batchbar" [class.show]="selected.size > 0">
     <span class="batch-count">已选 {{ selected.size }} 项</span>

ui/src/app/library-browser.component.sass

@@ -252,11 +252,13 @@
   gap: 2px
 
 // Grid view
-.grid
+.grid-wrap
   flex: 1
   min-height: 0
   overflow-y: auto
   padding: 14px
+
+.grid
   display: grid
   grid-template-columns: repeat(auto-fill, minmax(218px, 1fr))
   gap: 14px