feat(ui): add /settings command and UI panel (#4738)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/cli/src/ui/commands/settingsCommand.ts

@@ -0,0 +1,17 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { CommandKind, OpenDialogActionReturn, SlashCommand } from './types.js';
+
+export const settingsCommand: SlashCommand = {
+  name: 'settings',
+  description: 'View and edit Gemini CLI settings',
+  kind: CommandKind.BUILT_IN,
+  action: (_context, _args): OpenDialogActionReturn => ({
+    type: 'dialog',
+    dialog: 'settings',
+  }),
+};