feat: Add auto-approval for mode switching

Implements automatic approval for mode switching operations when enabled, following
existing auto-approval patterns in the codebase.

Implementation:
- Added `alwaysAllowModeSwitch` to state management
- Updated `isAutoApproved` function in ChatView to handle mode switch requests
- Added mode switch option to AutoApproveMenu with appropriate handler
- Integrated with existing auto-approval flow

Tests:
- Added three test cases in ChatView.auto-approve.test.tsx:
  1. Verifies mode switch auto-approval when enabled
  2. Verifies no auto-approval when mode switch setting is disabled
  3. Verifies no auto-approval when global auto-approval is disabled

The implementation follows existing patterns for other auto-approve features
(read, write, browser, etc.) to maintain consistency in the codebase.

src/shared/ExtensionMessage.ts

@@ -91,6 +91,7 @@ export interface ExtensionState {
 	alwaysAllowBrowser?: boolean
 	alwaysAllowMcp?: boolean
 	alwaysApproveResubmit?: boolean
+	alwaysAllowModeSwitch?: boolean
 	requestDelaySeconds: number
 	uriScheme?: string
 	allowedCommands?: string[]