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/components/chat/Chat.svelte

@@ -2230,7 +2230,7 @@
 
 <svelte:head>
 	<title>
-		{$chatTitle
+		{$settings.useChatTitleAsTabTitle !== false && $chatTitle
 			? `${$chatTitle.length > 30 ? `${$chatTitle.slice(0, 30)}...` : $chatTitle} • ${$WEBUI_NAME}`
 			: `${$WEBUI_NAME}`}
 	</title>