Add comprehensive GitHub Copilot instructions for portfolio website development

[Copilot]

This PR adds a comprehensive .github/copilot-instructions.md file that provides GitHub Copilot with detailed guidance on how to work effectively with this portfolio website codebase.

What's Added

The instructions file provides:

• Quick start commands for serving the static website locally using Python's HTTP server
• Complete development workflow for editing HTML, CSS, and JavaScript files
• Manual testing procedures with step-by-step validation scenarios for navigation, forms, and responsive design
• File structure documentation explaining the project's HTML5/CSS3/JavaScript architecture
• Performance benchmarks with actual timing measurements for all operations
• Troubleshooting guides for common development issues

Technology Stack Confirmed

Through comprehensive testing, the instructions document that this is a pure static website requiring:

• No build tools or compilation steps
• No package managers (npm, yarn) or dependencies
• Direct file editing with immediate browser refresh
• Simple Python HTTP server for local development

Validation Performed

Every single command and instruction has been 100% validated through manual testing:

✅ Server setup: python3 -m http.server 8000 starts in 1-2 seconds
✅ Navigation: Smooth scrolling and active state highlighting work correctly
✅ Form functionality: Validation and submission with proper alerts and form reset
✅ Responsive design: Layout adapts correctly from desktop to mobile viewports
✅ HTML validation: Syntax validation passes using Python's HTML parser
✅ Browser console: Shows expected "Portfolio website loaded successfully!" message

Key Features

The instructions follow best practices with:

• Imperative tone: "Run this command", "Do not do this" format
• Explicit timing guidance: "NEVER CANCEL" warnings with timeout recommendations
• Expected results: What developers should see after each step
• Error handling: Documentation of expected 404s for placeholder images

This ensures that GitHub Copilot will have complete context for working with the portfolio website, from initial setup through development, testing, and deployment.

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.