Fix chatbot error handling: specific error messages and login loop fix

[PRAteek-singHWY]

This PR addresses Issue #692 by improving the error handling logic in the Chatbot component. It replaces generic error messages with specific feedback from the server and fixes a potential infinite loop in the authentication check.

Changes Overview

Feature	Before	After	Benefit
User Feedback	Generic error: "Document could not be loaded"	Specific Error: Displays the actual error message from the server (e.g., "Network Error", "Rate limit exceeded").	Users know exactly why the request failed and what to do next.
Error Logic	Ignored HTTP error codes (400/500) and failed silently on JSON parsing.	Robust Parsing: Checks !response.ok, parses JSON or text errors, and throws meaningful exceptions.	Prevents silent failures and catches server-side validation issues.
Stability	login() called directly in render body.	Fixed: login() called inside useEffect.	Prevents potential infinite re-render loops and improves app performance.
Code Cleanup	Unused import LoadingAndErrorIndicator present.	Cleaned: Removed unused import.	Cleaner codebase.

How to Test

1. Network Error: Disconnect internet or block the network request in DevTools. Verify the UI says "Network error..." instead of a generic message.
2. Server Error: If possible, trigger a 500 or 400 error from the backend. Verify the UI displays the specific message returned by the API.
3. Normal Usage: Verify that chatting works normally when no errors occur.

fixes #692