✨ Set up Copilot instructions for better AI assistance

[Copilot]

This PR implements comprehensive Copilot instructions to enhance GitHub Copilot's effectiveness when working with this repository, following the best practices outlined in the GitHub documentation.

What's Added

.github/copilot-instructions.md - A comprehensive 173-line guide that provides Copilot with detailed context about:

• Project Architecture: Multi-AI chatbot application built with Streamlit, integrating OpenAI, MistralAI, Anthropic, and Cohere APIs
• Document Processing: LangChain-based document handling with Chroma vector database for PDF, text, CSV, and web content
• Core Components: Detailed breakdown of main.py and document_loader.py with function APIs and usage patterns

Development Guidelines Included

The instructions provide specific guidance for:

• AI Provider Integration: Patterns for adding new providers, error handling, and cost tracking
• Streamlit Best Practices: Session state management, UI component usage, and file handling
• Document Processing Workflows: Text splitting, embedding creation, and similarity search
• Code Standards: PEP 8 compliance, type hints, docstrings, and consistent formatting

Technical Documentation

• Complete Function Reference: All key functions documented with parameters and usage
• Environment Setup: Required API keys and dependency installation steps
• Common Issues: Troubleshooting guide for API keys, document processing, and model availability
• Security Considerations: Proper handling of sensitive data and API credentials

Repository Improvements

• Updated .gitignore: Added Python cache files and build artifacts to prevent accidental commits
• Dependency Issues Identified: Documented missing langchain-chroma dependency with installation instructions

Impact

With these instructions in place, GitHub Copilot will be able to:

• Provide more accurate code suggestions that follow the project's patterns
• Understand the multi-AI provider architecture and integration patterns
• Suggest appropriate error handling and cost tracking implementations
• Maintain consistency with existing Streamlit and LangChain usage

This enhancement will significantly improve the development experience for contributors working on the chatbot application.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #3

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[Copilot]

Pull Request Overview

This PR implements comprehensive GitHub Copilot instructions to enhance AI assistance effectiveness for the multi-AI chatbot repository. The addition provides detailed context about the project's architecture, development patterns, and best practices to help Copilot generate more accurate and consistent code suggestions.

• Comprehensive documentation covering the multi-AI provider architecture and key components
• Development guidelines for AI integration patterns, Streamlit best practices, and code standards
• Environment setup instructions and troubleshooting guide for common issues

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_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

There's a trailing space after 'your_mistral_api_key' that should be removed for consistency with other environment variable examples.

Suggested change

	MISTRAL=your_mistral_api_key
	MISTRAL=your_mistral_api_key