🎨 style(table): customize table scrollbar appearance

Enhance table scrollbar visual design with lighter and thinner styling for better user experience.

Changes:
- Add custom scrollbar styling for .semi-table-body
- Set scrollbar dimensions to 6px width/height
- Apply lighter color using rgba(var(--semi-grey-2), 0.3) with 30% opacity
- Add hover effect with 50% opacity for better interaction feedback
- Use 2px border radius for smoother appearance
- Keep scrollbar track transparent for clean look
- Utilize Semi Design color variables for theme consistency

The new scrollbar design provides a more elegant and less intrusive horizontal scrolling experience across all data tables.

web/src/index.css

@@ -339,6 +339,25 @@ code {
 }
 
 /* ==================== 滚动条样式统一管理 ==================== */
+/* 表格滚动条样式 */
+.semi-table-body::-webkit-scrollbar {
+  width: 6px;
+  height: 6px;
+}
+
+.semi-table-body::-webkit-scrollbar-thumb {
+  background: rgba(var(--semi-grey-2), 0.3);
+  border-radius: 2px;
+}
+
+.semi-table-body::-webkit-scrollbar-thumb:hover {
+  background: rgba(var(--semi-grey-2), 0.5);
+}
+
+.semi-table-body::-webkit-scrollbar-track {
+  background: transparent;
+}
+
 /* 隐藏模型设置区域的滚动条 */
 .model-settings-scroll::-webkit-scrollbar,
 .thinking-content-scroll::-webkit-scrollbar,