feat(ui): search in the agent model dropdown (#352)

Select gains an optional search box that filters its options; the agent model pickers use it, so long model lists can be filtered instead of scrolled. Keyboard navigation and type-ahead work on the filtered list, and the popup keeps its width while filtering.

Co-authored-by: dimassfeb-09 <[email protected]>

src/platform/locales/text/zh.json

@@ -3431,6 +3431,7 @@
   "Chart Settings": "图表设置",
   "No numeric values to plot": "没有可绘制的数值",
   "Search": "搜索",
+  "Search…": "搜索…",
   "Statements": "语句",
   "No statements": "没有语句",
   "Statement": "语句",