Add Copilot instructions for repository

[Copilot]

Configures GitHub Copilot coding agent instructions per best practices to provide context-aware suggestions for this repository.

Changes

• Created .github/copilot-instructions.md with comprehensive repository guidelines:
  • Tech stack: React 18 + TypeScript + Vite (frontend), FastAPI + Python 3.11 (backend), Azure deployment
  • Development commands for local setup, building, and Docker workflows
  • Coding standards: functional React components, PEP 8 for Python, type hints required
  • Architecture patterns: component-based frontend with TailwindCSS slate theme, RESTful API with multi-model support
  • Security: environment variables for Azure OpenAI keys, no hardcoded secrets
  • Common patterns: adding components to /components/*.tsx, configuring AI models in MODELS dictionary
  • Styling guidelines: bg-slate-950 backgrounds, border-slate-800 borders, lucide-react icons

This enables Copilot to generate code consistent with existing patterns and understand the Azure AI orchestration architecture.

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 ✨ Set up Copilot instructions #27

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.