Add comprehensive SETUP.md with detailed setup and deployment instructions

[Copilot]

This PR adds a comprehensive SETUP.md file that provides first-time users with detailed guidance on setting up their development environment for the Sustineo project.

What's Added

The new SETUP.md file includes:

• Project Overview: Clear summary of Sustineo as an AI-powered personal assistant with voice capabilities, linking back to the main README
• API Backend Setup: Step-by-step instructions for setting up the Python FastAPI backend including:
  • Virtual environment creation
  • Dependency installation
  • Environment variable configuration for Azure services
• Web Frontend Setup: Detailed Node.js/React setup instructions with npm dependency management
• Running Everything Together: Multiple options for starting services including automated scripts and manual startup
• GitHub Actions Deployment: Comprehensive documentation of the Azure Container Apps deployment process including:
  • Detailed workflow explanations for both API and web deployments
  • Required secrets and environment setup
  • Manual deployment alternatives

Key Features

• Quick Start with Dev Containers: Streamlined setup using VS Code dev containers (recommended approach)
• Manual Setup Alternative: Complete instructions for developers who prefer manual configuration
• Environment Variables Guide: Clear documentation of all required Azure service credentials
• Troubleshooting Section: Common issues and solutions for setup problems
• Development Workflow: Testing, building, and development best practices

The documentation covers both development setup and production deployment, making it easy for new contributors to get started while also serving as a reference for deployment procedures.

Fixes #58.

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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.