Restore RemoteSearchMenuUI for Electron overlay search menu (#2134)

## Summary

Restore `RemoteSearchMenuUI` usage in Electron so the completion menu
renders in a separate `WebContentsView` that can overlay beyond the chat
view bounds.

When PR #1933 added inline ghost text completions, it replaced the
`RemoteSearchMenuUI`/`LocalSearchMenuUI` branching with
`InlineSearchMenuUI`/`LocalSearchMenuUI`, leaving `RemoteSearchMenuUI`
as dead code. The remote search menu infrastructure (IPC handlers,
`electronSearchMenuUI.ts`, `searchMenuView.ts`, preload bindings) was
never removed and remains fully intact.

## Changes

- **`packages/shell/src/renderer/src/search.ts`**: When not in inline
mode, use `RemoteSearchMenuUI` in Electron (via `isElectron()` check)
and fall back to `LocalSearchMenuUI` in non-Electron environments. This
matches the original behavior before #1933.

Author: curtisman

ts/packages/shell/src/renderer/src/search.ts

@@ -1,9 +1,11 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+import { isElectron } from "./main";
 import { SearchMenuBase } from "./searchMenuBase";
 import { InlineSearchMenuUI } from "./searchMenuUI/inlineSearchMenuUI";
 import { LocalSearchMenuUI } from "./searchMenuUI/localSearchMenuUI";
+import { RemoteSearchMenuUI } from "./searchMenuUI/remoteSearchMenuUI";
 import {
     SearchMenuItem,
     SearchMenuPosition,
@@ -29,7 +31,9 @@ export class SearchMenu extends SearchMenuBase {
         if (this.searchMenuUI === undefined) {
             this.searchMenuUI = this.inline
                 ? new InlineSearchMenuUI(this.onCompletion, this.textEntry!)
-                : new LocalSearchMenuUI(this.onCompletion);
+                : isElectron()
+                  ? new RemoteSearchMenuUI(this.onCompletion)
+                  : new LocalSearchMenuUI(this.onCompletion);
         }
         this.searchMenuUI.update({ position, prefix, items });
     }