refactor: enhance chat functionality with new tools and attachment handling

- Updated system prompt to clarify usage of the display_image tool, emphasizing valid URL requirements and prohibiting user-uploaded image displays.
- Introduced write_todos tool for creating and updating planning lists, with detailed usage instructions and examples.
- Enhanced message handling to persist attachments and mentioned documents, ensuring they survive page reloads.
- Improved UI components to integrate the new write_todos tool and ensure consistent user experience across chat interactions.

surfsense_web/components/assistant-ui/thread.tsx

@@ -571,7 +571,7 @@ const Composer: FC = () => {
 				<div ref={editorContainerRef} className="aui-composer-input-wrapper px-3 pt-3 pb-6">
 					<InlineMentionEditor
 						ref={editorRef}
-						placeholder="Ask SurfSense (type @ to mention docs)"
+						placeholder="Ask SurfSense or @mention docs"
 						onMentionTrigger={handleMentionTrigger}
 						onMentionClose={handleMentionClose}
 						onChange={handleEditorChange}