feat: implement document mention extraction and management in new chat

- Added functionality to extract and manage mentioned documents within the new chat interface.
- Introduced new atoms for storing mentioned documents and their mappings to user messages.
- Enhanced the message persistence logic to include mentioned documents, ensuring they are displayed correctly in the chat.
- Updated the UI components to support document mentions, including a refined document selection interface.
- Improved state management for document mentions to ensure a seamless user experience.

surfsense_web/atoms/chat/mentioned-documents.atom.ts

@@ -1,6 +1,7 @@
 "use client";
 
 import { atom } from "jotai";
+import type { Document } from "@/contracts/types/document.types";
 
 /**
  * Atom to store the IDs of documents mentioned in the current chat composer.
@@ -8,3 +9,24 @@ import { atom } from "jotai";
  */
 export const mentionedDocumentIdsAtom = atom<number[]>([]);
 
+/**
+ * Atom to store the full document objects mentioned in the current chat composer.
+ * This persists across component remounts.
+ */
+export const mentionedDocumentsAtom = atom<Document[]>([]);
+
+/**
+ * Simplified document info for display purposes
+ */
+export interface MentionedDocumentInfo {
+	id: number;
+	title: string;
+	document_type: string;
+}
+
+/**
+ * Atom to store mentioned documents per message ID.
+ * This allows displaying which documents were mentioned with each user message.
+ */
+export const messageDocumentsMapAtom = atom<Record<string, MentionedDocumentInfo[]>>({});
+