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`).

src/blog/post-5.md

@@ -0,0 +1,64 @@
+---
+title: 'Fixing GitHub Copilot CLI System Vault Error with systemd'
+pubDate: 2026-01-02
+author: 'Nakahara Daisuke'
+tags: ["GitHub", "AI"]
+---
+
+When installing GitHub Copilot CLI, you may encounter the error message: `The system vault (keychain, keyring, password manager, etc.) is not available. You may need to install one.` The solution was documented in [this issue](https://github.com/github/copilot-cli/issues/49).
+
+This article explains how to resolve this issue using `systemd`.
+
+### Install via Apt
+
+```bash
+$ sudo apt update
+```
+```bash
+$ sudo apt install -y \
+  gnome-keyring \
+  libsecret-1-0 \
+  libsecret-tools \
+  seahorse
+```
+
+### Verify systemd is running
+```bash
+$ systemctl is-system-running
+```
+
+### Check if the user service is enabled
+```bash
+$ systemctl --user status gnome-keyring-daemon
+○ gnome-keyring-daemon.service - GNOME Keyring daemon
+     Loaded: loaded (/usr/lib/systemd/user/gnome-keyring-daemon.service; enabled; preset: enabled)
+     Active: inactive (dead)
+TriggeredBy: ○ gnome-keyring-daemon.socket
+```
+```bash
+$ systemctl --user enable gnome-keyring-daemon
+```
+```bash
+$ systemctl --user start gnome-keyring-daemon
+```
+```bash
+$ systemctl --user status gnome-keyring-daemon
+● gnome-keyring-daemon.service - GNOME Keyring daemon
+     Loaded: loaded (/usr/lib/systemd/user/gnome-keyring-daemon.service; enabled; preset: enabled)
+     Active: active (running) since Fri 2026-01-02 08:36:46 JST; 3s ago
+ Invocation: d830e5563e974edc9265650d11dfa086
+TriggeredBy: ● gnome-keyring-daemon.socket
+   Main PID: 5222 (gnome-keyring-d)
+      Tasks: 5 (limit: 9422)
+     Memory: 3.4M (peak: 3.9M)
+        CPU: 37ms
+     CGroup: /user.slice/user-1000.slice/user@1000.service/app.slice/gnome-keyring-daemon.service
+             └─5222 /usr/bin/gnome-keyring-daemon --foreground --components=pkcs11,secrets --control-directory=/run/user/1000/keyring
+
+Jan 02 08:36:46 hostname systemd[649]: Started gnome-keyring-daemon.service - GNOME Keyring daemon.
+Jan 02 08:36:46 hostname gnome-keyring-daemon[5222]: GNOME_KEYRING_CONTROL=/run/user/1000/keyring
+Jan 02 08:36:46 hostname gnome-keyring-daemon[5222]: another secret service is running
+Jan 02 08:36:46 hostname gnome-keyring-d[5222]: another secret service is running
+```
+
+> **Note**: This article was translated from Japanese to English and reviewed with the assistance of AI (GitHub Copilot).

src/components/Footer.astro

@@ -16,5 +16,5 @@
 </style>
 
 <footer>
-    <p class="legal-information">&copy; 2025 Nakahara Daisuke</p>
+    <p class="legal-information">&copy; 2026 Nakahara Daisuke — Built with <a href="https://astro.build" target="_blank" rel="noopener">Astro</a></p>
 </footer>

src/components/Navigation.astro

@@ -7,7 +7,7 @@
     <a href="/about/">About</a>
     <a href="/blog/">Articles</a>
     <a href="/tags/">Tags</a>
-    <a href="https://git.n-daisuke897.com/" target="_blank">
+    <a href="https://git.n-daisuke897.com/nakada0907/" target="_blank">
         <img src="/icon/simple-icons--forgejo.svg" alt="Forgejo Icon">
     </a>
 </div>

src/layouts/MarkdownPostLayout.astro

@@ -49,18 +49,27 @@ const optionsForDate = {
 
   .markdown-content {
     font-family: sans-serif;
-    font-size: 1.2rem;
-    line-height: 2.5;
+    font-size: 1.1rem;
+    line-height: 1.8;
   }
 
   .markdown-content h1 {
-    font-size: 1.9rem;
+    font-size: 1.6rem;
+    margin-top: 2rem;
+    margin-bottom: 1rem;
+    line-height: 1.3;
   }
   .markdown-content h2 {
-    font-size: 1.75rem;
+    font-size: 1.4rem;
+    margin-top: 1.8rem;
+    margin-bottom: 0.8rem;
+    line-height: 1.3;
   }
   .markdown-content h3 {
-    font-size: 1.5rem;
+    font-size: 1.2rem;
+    margin-top: 1.5rem;
+    margin-bottom: 0.6rem;
+    line-height: 1.3;
   }
 
 </style>

src/pages/index.astro

@@ -4,6 +4,7 @@ import BlogPost from "../components/BlogPost.astro";
 import { getCollection } from "astro:content";
 const pageTitle = "Naputo";
 const allPosts = await getCollection("blog");
+const sortedPosts = allPosts.sort((a, b) => b.data.pubDate.valueOf() - a.data.pubDate.valueOf());
 ---
 
 <style>
@@ -41,7 +42,7 @@ const allPosts = await getCollection("blog");
 	<h3 class="header-new-posts">New Posts</h3>
 	<div class="new-articles">
 		{
-			allPosts.slice(0, 6).map((post: any) => (
+			sortedPosts.slice(0, 5).map((post: any) => (
 				<BlogPost
 					url={`/posts/${post.id}/`}
 					title={post.data.title}