Add comprehensive test suite

[JiwaniZakir]

Problem

The project has only a single smoke test. The core chatbot logic (message handling, prompt construction, streaming) has no test coverage.

Proposed Solution

• Add unit tests for the Chatbot component's message flow
• Test the prompt construction logic (knowledge base + user message)
• Test error handling (API failures, network errors)
• Test the loading state and streaming behavior
• Use MSW (Mock Service Worker) or manual fetch mocks for API calls