Add CLAUDE.md

Add Claude Code guidance file with commands and architecture overview

Author: heimann

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Commands
+
+- `npm run dev` - Start local dev server at localhost:4321
+- `npm run build` - Run type checking and build to `./dist/`
+- `just run` - Alias for `npm run dev`
+
+## Architecture
+
+This is a personal website (dmeh.net) built with Astro 4 and Tailwind CSS.
+
+**Layout structure:**
+- `src/layouts/BaseLayout.astro` - Main layout with Nav, uses Inter font
+- `src/layouts/MarkdownPostLayout.astro` - Layout for markdown blog posts
+
+**Pages:**
+- `src/pages/index.astro` - Homepage
+- `src/pages/writing.astro` - Blog post listing
+- `src/pages/books.astro` - Book list
+- `src/pages/posts/` - Markdown blog posts
+
+**Components:**
+- `src/components/Nav.astro` - Navigation sidebar
+- `src/components/NavLink.astro` - Styled nav links
+
+## Formatting
+
+Uses Prettier with prettier-plugin-astro for .astro files.