chore: add Copilot instructions for project guidance

Add Copilot-specific instructions documenting project overview, tech stack,
  structure, development guidelines, and best practices for AI-assisted development.

.github/copilot-instructions.md

@@ -0,0 +1,59 @@
+# Copilot Instructions for n-daisuke897-blog
+
+## Project Overview
+This is a personal blog named "Naputo" built with Astro and Preact. The blog is designed to publish articles and content with a modern static site generation approach.
+
+**Repository**: https://git.n-daisuke897.com/nakada0907/n-daisuke897-blog
+
+## Tech Stack
+- **Framework**: Astro 5.x
+- **UI Library**: Preact 10.x for interactive components
+- **Language**: TypeScript
+- **Build Tool**: Astro CLI
+- **RSS**: @astrojs/rss for RSS feed generation
+- **Linting**: ESLint with TypeScript and Astro plugins
+
+## Project Structure
+- `src/`: Source code
+  - `pages/`: Astro pages (routing based on file structure)
+  - `layouts/`: Layout components
+  - `components/`: Reusable components
+  - `blog/`: Blog content
+  - `styles/`: Global styles
+  - `scripts/`: Utility scripts
+  - `content.config.ts`: Content collection configuration
+- `public/`: Static assets (images, fonts, etc.)
+- `dist/`: Build output directory
+- `buildspec.yml`: AWS CodeBuild configuration
+
+## Development Guidelines
+
+### Commands
+- `npm install`: Install dependencies
+- `npm run dev`: Start local development server at `localhost:4321`
+- `npm run build`: Build production site to `./dist/`
+- `npm run preview`: Preview production build locally
+- `npm run astro`: Run Astro CLI commands
+
+### Coding Standards
+- Use TypeScript for all new code
+- Follow the ESLint configuration provided
+- Use Preact components for interactive UI elements
+- Keep components modular and reusable
+- Use Astro's component syntax for static content
+
+### File Naming
+- Use kebab-case for file names
+- Use PascalCase for component names
+- Use `.astro` extension for Astro components
+- Use `.tsx` extension for Preact components
+
+### Best Practices
+- Prefer static generation over client-side rendering when possible
+- Use Astro's content collections for blog posts
+- Optimize images and assets before adding to `public/`
+- Keep bundle size minimal - Astro ships zero JS by default
+- Use Preact only when client interactivity is needed
+
+## Deployment
+This project uses AWS CodeBuild for deployment (see `buildspec.yml`).