feat: add toggle to show/hide chat title in browser tab

This commit introduces a new setting in the Interface settings that allows users to control whether the chat title is used as the browser's tab title.

The following changes were made:
- Added `useChatTitleAsTabTitle` to the `Settings` type in `src/lib/stores/index.ts`.
- Added a toggle switch in `src/lib/components/chat/Settings/Interface.svelte` to manage this new setting.
- Updated `src/lib/components/chat/Chat.svelte` to conditionally set the document title based on the `useChatTitleAsTabTitle` setting.

src/lib/stores/index.ts

@@ -184,6 +184,7 @@ type Settings = {
 	notificationEnabled?: boolean;
 	highContrastMode?: boolean;
 	title?: TitleSettings;
+	useChatTitleAsTabTitle?: boolean;
 	splitLargeDeltas?: boolean;
 	chatDirection?: 'LTR' | 'RTL' | 'auto';
 	ctrlEnterToSend?: boolean;