Add CLAUDE.md for Claude Code guidance

Provides essential project context including:
- Single-file architecture overview
- Development instructions (no build process)
- AlpineJS component structure
- Code style conventions

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.
+
+## Project Overview
+
+A browser-based QR code label generator for Paperless-ngx Archive Serial Numbers (ASN). The entire application is a single `index.html` file with no build process.
+
+## Development
+
+**No build tools required** - Open `index.html` directly in a browser or serve it with any static file server.
+
+The application uses CDN-hosted dependencies:
+- TailwindCSS (with forms and typography plugins)
+- AlpineJS 3.x
+
+## Architecture
+
+Single-page application using AlpineJS for reactivity. Key structure in `index.html`:
+
+- **`qrCodeApp()`** (line 255): AlpineJS component containing all application state and logic
+  - `generateLabels()`: Creates label data array with QR code URLs via external API (api.qrserver.com)
+  - `printLabels()`: Triggers browser print dialog
+  - Generates 189 labels per sheet (7 columns × 27 rows)
+
+- **Print styling**: Uses CSS `@page` rule for A4 paper with zero margins (requires Chrome/Chromium)
+
+- **Label format**: Hardcoded for Avery L4731REV-25 labels with specific dimensions (25.4mm × 10mm per label)
+
+## Code Style
+
+- 2 spaces for indentation
+- LF line endings
+- UTF-8 encoding