feat: add CLAUDE.md for LLM-assisted development guidance (#23946)

CLAUDE.md

@@ -0,0 +1,83 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Dify is an open-source platform for developing LLM applications with an intuitive interface combining agentic AI workflows, RAG pipelines, agent capabilities, and model management.
+
+The codebase consists of:
+- **Backend API** (`/api`): Python Flask application with Domain-Driven Design architecture
+- **Frontend Web** (`/web`): Next.js 15 application with TypeScript and React 19
+- **Docker deployment** (`/docker`): Containerized deployment configurations
+
+## Development Commands
+
+### Backend (API)
+
+All Python commands must be prefixed with `uv run --project api`:
+
+```bash
+# Start development servers
+./dev/start-api                   # Start API server
+./dev/start-worker                # Start Celery worker
+
+# Run tests
+uv run --project api pytest      # Run all tests
+uv run --project api pytest tests/unit_tests/     # Unit tests only
+uv run --project api pytest tests/integration_tests/  # Integration tests
+
+# Code quality
+./dev/reformat                    # Run all formatters and linters
+uv run --project api ruff check --fix ./    # Fix linting issues
+uv run --project api ruff format ./         # Format code
+uv run --project api mypy .                 # Type checking
+```
+
+### Frontend (Web)
+
+```bash
+cd web
+pnpm lint                         # Run ESLint
+pnpm eslint-fix                   # Fix ESLint issues
+pnpm test                         # Run Jest tests
+```
+
+## Testing Guidelines
+
+### Backend Testing
+- Use `pytest` for all backend tests
+- Write tests first (TDD approach)
+- Test structure: Arrange-Act-Assert
+
+## Code Style Requirements
+
+### Python
+- Use type hints for all functions and class attributes
+- No `Any` types unless absolutely necessary
+- Implement special methods (`__repr__`, `__str__`) appropriately
+
+### TypeScript/JavaScript  
+- Strict TypeScript configuration
+- ESLint with Prettier integration
+- Avoid `any` type
+
+## Important Notes
+
+- **Environment Variables**: Always use UV for Python commands: `uv run --project api <command>`
+- **Comments**: Only write meaningful comments that explain "why", not "what"
+- **File Creation**: Always prefer editing existing files over creating new ones
+- **Documentation**: Don't create documentation files unless explicitly requested
+- **Code Quality**: Always run `./dev/reformat` before committing backend changes
+
+## Common Development Tasks
+
+### Adding a New API Endpoint
+1. Create controller in `/api/controllers/`
+2. Add service logic in `/api/services/`
+3. Update routes in controller's `__init__.py`
+4. Write tests in `/api/tests/`
+
+## Project-Specific Conventions
+
+- All async tasks use Celery with Redis as broker