docs: add CLAUDE.md for Claude Code quick reference

Add project-specific context file for Claude Code with quick commands,
key files reference, project structure overview, and code patterns.

CLAUDE.md

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+# CLAUDE.md
+
+> Quick reference for Claude Code when working on prompts.chat
+
+## Project Overview
+
+**prompts.chat** is a social platform for AI prompts built with Next.js 16 App Router, React 19, TypeScript, and PostgreSQL/Prisma. It allows users to share, discover, and collect prompts.
+
+For detailed agent guidelines, see [AGENTS.md](AGENTS.md).
+
+## Quick Commands
+
+```bash
+# Development
+npm run dev              # Start dev server at localhost:3000
+npm run build            # Production build (runs prisma generate)
+npm run lint             # Run ESLint
+
+# Database
+npm run db:migrate       # Run Prisma migrations
+npm run db:push          # Push schema changes
+npm run db:studio        # Open Prisma Studio
+npm run db:seed          # Seed database
+
+# Type checking
+npx tsc --noEmit         # Check TypeScript types
+```
+
+## Key Files
+
+| File | Purpose |
+|------|---------|
+| `prompts.config.ts` | Main app configuration (branding, theme, auth, features) |
+| `prisma/schema.prisma` | Database schema |
+| `src/lib/auth/index.ts` | NextAuth configuration |
+| `src/lib/db.ts` | Prisma client singleton |
+| `messages/*.json` | i18n translation files |
+
+## Project Structure
+
+```
+src/
+├── app/              # Next.js App Router pages
+│   ├── (auth)/       # Login, register
+│   ├── api/          # API routes
+│   ├── prompts/      # Prompt CRUD pages
+│   └── admin/        # Admin dashboard
+├── components/       # React components
+│   ├── ui/           # shadcn/ui base components
+│   └── prompts/      # Prompt-related components
+└── lib/              # Utilities and config
+    ├── ai/           # OpenAI integration
+    ├── auth/         # NextAuth setup
+    └── plugins/      # Auth and storage plugins
+```
+
+## Code Patterns
+
+- **Server Components** by default, `"use client"` only when needed
+- **Translations:** Use `useTranslations()` or `getTranslations()` from next-intl
+- **Styling:** Tailwind CSS with `cn()` utility for conditional classes
+- **Forms:** React Hook Form + Zod validation
+- **Database:** Prisma client from `@/lib/db`
+
+## Before Committing
+
+1. Run `npm run lint` to check for issues
+2. Add translations for any user-facing text
+3. Use existing UI components from `src/components/ui/`
+4. Never commit secrets (use `.env`)