Export Chat Conversation as Text File

[avishek0769]

Summary

Allow users to export full conversation content to a .txt file.

Problem

Users currently cannot download chat transcripts for offline review, reporting, or sharing.

Expected Solution

Add export action in chat UI that builds a readable text transcript with timestamps, roles, model name, and sources. Should be formatted well. Perform exports in server-side always to handle large conversations without blocking the UI.

Scope

• src/pages/ChatPage.tsx
• src/lib/api.ts

Acceptance Criteria

• Export button is visible on chat page and downloads .txt file.
• Export includes ordered user/assistant messages with timestamps.
• Export is correctly encoded (UTF-8) and readable on common editors.
• Large conversations are handled without UI freeze.
• Export is handled in server-side route that generates and streams the file.