chore: add CLAUDE.md

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
+
+**diffractwd.com** — Product website for DiffractWD, an X-ray diffraction analysis tool.
+
+**Repository:** `vreshch/diffractwd.com`
+**Default Branch:** `master`
+**Framework:** Next.js 15 App Router
+
+## Development Commands
+
+```bash
+npm install              # Install dependencies
+npm run dev              # Start Next.js dev server
+npm run build            # Production build
+npm test                 # Run Vitest unit tests
+npm run test:e2e         # Run Playwright E2E tests
+npm run lint             # Next.js ESLint
+npm run format:check     # Prettier check
+npm run verify           # Full pipeline: type-check + lint + build + test
+```
+
+## Architecture
+
+```
+src/
+├── app/                 # Next.js App Router pages and layouts
+├── components/          # React components
+├── data/                # Static data and content
+├── lib/                 # Utilities and helpers
+└── test/                # Test utilities
+```
+
+### Key Patterns
+
+- **Server Components** by default, `'use client'` only when needed
+- **Tailwind CSS v4** with `class-variance-authority` for variants
+- **Static-first** — marketing content with minimal client-side JS
+- Port 3001 in production
+
+### Key Dependencies
+
+- Next.js 15, React 19, Tailwind CSS v4
+- `sharp` — Image optimization
+- `class-variance-authority`, `clsx`, `tailwind-merge` — Styling utilities
+
+## Testing
+
+- **Unit:** Vitest — component and utility tests
+- **E2E:** Playwright — page navigation and visual tests
+
+## Deployment
+
+Docker container deployed via Docker Swarm behind Traefik. **Never deploy manually** — CI handles it on merge to master.
+
+## Standards
+
+See [root CLAUDE.md](../../CLAUDE.md) for tech standards and [showcase CLAUDE.md](../CLAUDE.md) for portfolio workflow rules.