🚀 feat: enhance model testing UI with bulk selection, copy & success-filter buttons (#1288)

* ChannelsTable
  - Added row-level checkboxes to the model-testing table for multi-selection
  - Implemented cross-page “Select All / Deselect All” via rowSelection.onSelectAll
  - Introduced allSelectingRef to ignore redundant onChange after onSelectAll
  - Added “Copy Selected” button to copy chosen model names (comma-separated) using helpers.copy
  - Added “Select Successful” button to auto-tick all models that passed testing
  - Moved search bar and new action buttons into the modal title for better UX
  - Centralised page size constant MODEL_TABLE_PAGE_SIZE in channel.constants.js
  - Fixed pagination slicing and auto-page-switch logic during batch testing

* channel.constants
  - Exported MODEL_TABLE_PAGE_SIZE (default 10) for unified pagination control

This commit enables users to conveniently copy or filter successful models, fully supports cross-page bulk operations, and resolves previous selection inconsistencies.

Refs: #1288

web/src/index.css

@@ -375,6 +375,7 @@ code {
 }
 
 /* 隐藏卡片内容区域的滚动条 */
+.model-test-scroll,
 .card-content-scroll,
 .model-settings-scroll,
 .thinking-content-scroll,
@@ -385,6 +386,7 @@ code {
   scrollbar-width: none;
 }
 
+.model-test-scroll::-webkit-scrollbar,
 .card-content-scroll::-webkit-scrollbar,
 .model-settings-scroll::-webkit-scrollbar,
 .thinking-content-scroll::-webkit-scrollbar,