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

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

packages/cli/src/ui/hooks/slashCommandProcessor.test.ts

@@ -147,6 +147,7 @@ describe('useSlashCommandProcessor', () => {
         vi.fn(), // toggleCorgiMode
         mockSetQuittingMessages,
         vi.fn(), // openPrivacyNotice
+        vi.fn(), // openSettingsDialog
         vi.fn(), // toggleVimEnabled
         setIsProcessing,
       ),
@@ -864,6 +865,9 @@ describe('useSlashCommandProcessor', () => {
           vi.fn(), // toggleCorgiMode
           mockSetQuittingMessages,
           vi.fn(), // openPrivacyNotice
+
+          vi.fn(), // openSettingsDialog
+          vi.fn(), // toggleVimEnabled
           vi.fn().mockResolvedValue(false), // toggleVimEnabled
           vi.fn(), // setIsProcessing
         ),

packages/cli/src/ui/hooks/slashCommandProcessor.ts

@@ -50,6 +50,7 @@ export const useSlashCommandProcessor = (
   toggleCorgiMode: () => void,
   setQuittingMessages: (message: HistoryItem[]) => void,
   openPrivacyNotice: () => void,
+  openSettingsDialog: () => void,
   toggleVimEnabled: () => Promise<boolean>,
   setIsProcessing: (isProcessing: boolean) => void,
   setGeminiMdFileCount: (count: number) => void,
@@ -359,6 +360,11 @@ export const useSlashCommandProcessor = (
                     case 'privacy':
                       openPrivacyNotice();
                       return { type: 'handled' };
+                    case 'settings':
+                      openSettingsDialog();
+                      return { type: 'handled' };
+                    case 'help':
+                      return { type: 'handled' };
                     default: {
                       const unhandled: never = result.dialog;
                       throw new Error(
@@ -512,6 +518,7 @@ export const useSlashCommandProcessor = (
       openPrivacyNotice,
       openEditorDialog,
       setQuittingMessages,
+      openSettingsDialog,
       setShellConfirmationRequest,
       setSessionShellAllowlist,
       setIsProcessing,

packages/cli/src/ui/hooks/useSettingsCommand.ts

@@ -0,0 +1,25 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { useState, useCallback } from 'react';
+
+export function useSettingsCommand() {
+  const [isSettingsDialogOpen, setIsSettingsDialogOpen] = useState(false);
+
+  const openSettingsDialog = useCallback(() => {
+    setIsSettingsDialogOpen(true);
+  }, []);
+
+  const closeSettingsDialog = useCallback(() => {
+    setIsSettingsDialogOpen(false);
+  }, []);
+
+  return {
+    isSettingsDialogOpen,
+    openSettingsDialog,
+    closeSettingsDialog,
+  };
+}