add .github/copilot-instructions.md file

https://docs.github.com/en/copilot/customizing-copilot/adding-repository-custom-instructions-for-github-copilot

.github/copilot-instructions.md

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+# Project Information for GitHub Copilot
+
+This repository contains the source code for [jarv.is](https://jarv.is/), a personal website for Jake Jarvis built with Next.js.
+
+## Project Overview
+
+- **Type**: Personal website with blog
+- **Framework**: Next.js (uses latest features like App Router, Partial Prerendering)
+- **Primary Language**: TypeScript
+- **Styling**: Tailwind CSS
+- **Data Storage**: Upstash Redis
+- **Content**: MDX for blog posts with custom components
+- **Deployment**: Vercel
+
+## Project Structure
+
+```
+/
+├── app/           # Pages and layouts using Next.js App Router
+├── components/    # Reusable React components
+├── lib/           # Utility functions, configurations, and helpers
+├── notes/         # Blog posts written in MDX format along with any images
+└── public/        # Static assets
+```
+
+## Code Style & Conventions
+
+- **Formatting**: Prettier is used for code formatting
+- **Linting**: ESLint with custom configuration
+- **JavaScript/TypeScript**:
+  - Use double quotes for strings
+  - 2-space indentation (no tabs)
+  - Trailing commas in objects and arrays
+  - Maximum line length of 120 characters
+  - TypeScript is strictly typed
+- **React Components**:
+  - Prefer function components with hooks
+  - Use named exports for components
+  - Client components are marked with "use client" directive
+- **CSS**:
+  - Use Tailwind utility classes
+  - Custom CSS variables for theming (light/dark mode)
+  - `cn()` from `lib/utils.ts` utility for conditional class names
+
+## Preferred Solutions
+
+- When suggesting code changes, maintain the existing patterns and structure
+- **React Server Components when possible, Client Components when necessary**
+- MDX for content-heavy pages
+- Image optimization through Next.js Image component
+- Cache and revalidate data appropriately with tags
+
+## Other Notes
+
+- Dynamic theme switching (light/dark mode) is supported
+- Accessibility is important - maintain proper heading levels, skip links, etc.
+- Performance optimization is a priority (bundle sizes, image optimization, etc.)
+
+This document should be updated when significant architectural or dependency changes are made to the project.