feat: Add auto-accept indicator and toggle

- This commit introduces a visual indicator in the CLI to show when auto-accept for tool confirmations is enabled. Users can now also toggle this setting on/off using Shift + Tab.
- This addresses user feedback for better visibility and control over the auto-accept feature, improving the overall user experience.
- This behavior is similar to Claude Code, providing a familiar experience for users transitioning from that environment.
- Added tests for the new auto indicator hook.

Fixes https://b.corp.google.com/issues/413740468

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

@@ -0,0 +1,39 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { useState, useEffect } from 'react';
+import { useInput } from 'ink';
+import type { Config } from '@gemini-code/server';
+
+export interface UseAutoAcceptIndicatorArgs {
+  config: Config;
+}
+
+export function useAutoAcceptIndicator({
+  config,
+}: UseAutoAcceptIndicatorArgs): boolean {
+  const currentConfigValue = config.getAlwaysSkipModificationConfirmation();
+  const [showAutoAcceptIndicator, setShowAutoAcceptIndicator] =
+    useState(currentConfigValue);
+
+  useEffect(() => {
+    setShowAutoAcceptIndicator(currentConfigValue);
+  }, [currentConfigValue]);
+
+  useInput((_input, key) => {
+    if (key.tab && key.shift) {
+      const alwaysAcceptModificationConfirmations =
+        !config.getAlwaysSkipModificationConfirmation();
+      config.setAlwaysSkipModificationConfirmation(
+        alwaysAcceptModificationConfirmations,
+      );
+      // Update local state immediately for responsiveness
+      setShowAutoAcceptIndicator(alwaysAcceptModificationConfirmations);
+    }
+  });
+
+  return showAutoAcceptIndicator;
+}