Add CLAUDE.md file for Claude Code guidance (modelcontextprotocol#170)

## Summary
- Adds CLAUDE.md file to provide guidance for Claude Code instances
working with this repository
- Includes essential development commands and high-level architecture
overview
- Follows the standard format for Claude Code documentation

## Details
The CLAUDE.md file contains:
- Common development commands for building, running, testing, and
linting
- Architecture overview explaining the clean architecture pattern
- Request flow documentation
- Key interfaces and their implementations
- Authentication flow details
- Important design patterns used in the codebase

This will help future Claude Code instances be more productive when
working with the MCP Registry codebase.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <[email protected]>
Co-authored-by: Avinash Sridhar <[email protected]>

Author: 3 people

CLAUDE.md

@@ -0,0 +1,103 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Overview
+MCP Registry is a community-driven registry service for Model Context Protocol (MCP) servers. It provides a centralized repository for discovering and managing MCP implementations.
+
+## Common Development Commands
+
+### Build
+```bash
+# Build the registry application
+go build ./cmd/registry
+
+# Build with Docker
+docker build -t registry .
+
+# Build the publisher tool
+cd tools/publisher && ./build.sh
+```
+
+### Run
+```bash
+# Development with Docker Compose (recommended)
+docker compose up
+
+# Direct execution
+go run cmd/registry/main.go
+```
+
+### Test
+```bash
+# Unit tests
+go test -v -race -coverprofile=coverage.out -covermode=atomic ./internal/...
+
+# Integration tests
+./integrationtests/run_tests.sh
+
+# Test API endpoints
+./scripts/test_endpoints.sh
+
+# Test publish endpoint (requires GitHub token)
+export BEARER_TOKEN=your_github_token_here
+./scripts/test_publish.sh
+```
+
+### Lint
+```bash
+# Install golangci-lint if needed
+curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin v1.61.0
+
+# Run linting
+golangci-lint run --timeout=5m
+
+# Check formatting
+gofmt -s -l .
+```
+
+## Architecture Overview
+
+The codebase follows a clean architecture pattern:
+
+### Core Layers
+- **API Layer** (`internal/api/`) - HTTP handlers and routing
+- **Service Layer** (`internal/service/`) - Business logic implementation  
+- **Database Layer** (`internal/database/`) - Data persistence abstraction with MongoDB and in-memory implementations
+- **Domain Models** (`internal/model/`) - Core data structures
+- **Authentication** (`internal/auth/`) - GitHub OAuth integration
+
+### Request Flow
+1. HTTP requests enter through router (`internal/api/router/`)
+2. Handlers in `internal/api/handlers/v0/` validate and process requests
+3. Service layer executes business logic
+4. Database interface handles persistence
+5. JSON responses returned to clients
+
+### Key Interfaces
+- **Database Interface** (`internal/database/database.go`) - Abstracts data persistence with MongoDB and memory implementations
+- **RegistryService** (`internal/service/service.go`) - Business logic abstraction over database
+- **Auth Service** (`internal/auth/auth.go`) - GitHub OAuth token validation
+
+### Authentication Flow
+Publishing requires GitHub OAuth validation:
+1. Extract bearer token from Authorization header
+2. Validate token with GitHub API
+3. Verify repository ownership matches token owner
+4. Check organization membership if applicable
+
+### Design Patterns
+- **Factory Pattern** for service creation with dependency injection
+- **Repository Pattern** for database abstraction
+- **Context Pattern** for timeout management (5-second DB operations)
+- **Cursor-based Pagination** using UUIDs for stateless pagination
+
+## Environment Variables
+Key configuration for development:
+- `MCP_REGISTRY_DATABASE_URL` (default: `mongodb://localhost:27017`)
+- `MCP_REGISTRY_GITHUB_CLIENT_ID` 
+- `MCP_REGISTRY_GITHUB_CLIENT_SECRET`
+- `MCP_REGISTRY_LOG_LEVEL` (default: `info`)
+- `MCP_REGISTRY_SERVER_ADDRESS` (default: `:8080`)
+- `MCP_REGISTRY_SEED_IMPORT` (default: `true`)
+- `MCP_REGISTRY_SEED_FILE_PATH` (default: `data/seed.json`)