Add AI Instructions for Shop at Home Repository

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file to guide future AI coding agents working on the Shop at Home repository.

What's Added

Core Commands Documentation

• Build commands for all 4 frontend frameworks (Angular, React, Vue, Svelte)
• Test commands with current status (some require additional setup)
• Lint commands with framework-specific configurations
• Development scripts including SWA CLI integration for full-stack development
• API commands for both Azure Functions and Fastify backends

High-Level Architecture Overview

• Frontend: Angular 18, React 17, Vue 3, Svelte 4 with framework-specific state management
• Backend: Azure Functions (serverless) and Fastify API server options
• Deployment: Azure Static Web Apps and Azure Container Apps integration
• Build Tools: Angular CLI, Create React App, Vue CLI, Vite
• Styling: Bulma CSS framework with Font Awesome icons

Repository-Specific Style Rules

• Code formatting: Prettier configurations across all apps
• Linting: ESLint with Airbnb config in React/Vue, Angular ESLint patterns
• TypeScript: Strict mode usage and conventions
• Import patterns: Framework-specific module conventions
• Error handling: Consistent patterns for async operations
• Development ports: Framework-specific port assignments

Development Workflow

• Prerequisites and setup instructions
• SWA CLI integration for local full-stack development
• Current repository status with accurate build/test/lint capabilities
• API proxy configuration for local development

The instructions are based on actual repository analysis and testing, ensuring accuracy over assumptions.

Fixes #222.

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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.