docs: add CLAUDE.md with codebase overview for AI assistants

CLAUDE.md

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+# CLAUDE.md - Hazelnode
+
+Workflow automation platform built on Frappe framework with React frontend.
+
+## Tech Stack
+
+**Backend:** Python 3.10+, Frappe 15.0+, MariaDB 10.6+, Redis
+**Frontend:** React 18, TypeScript, Vite, TanStack Router/Query, Zustand, ReactFlow, Tailwind CSS
+
+## Project Structure
+
+```
+hazelnode/
+├── hazelnode/                 # Python backend (Frappe app)
+│   ├── hazelnode/doctype/     # Data models (workflows, nodes, logs)
+│   ├── nodes/                 # Node implementations
+│   │   ├── actions/           # Email, API call, condition, create/update doc, etc.
+│   │   ├── triggers/          # Webhook, schedule, document events
+│   │   └── __init__.py        # Abstract Node base class
+│   ├── fixtures/              # Standard node types (JSON)
+│   ├── hooks.py               # Frappe hooks
+│   └── api.py                 # REST endpoints
+├── frontend/                  # React app
+│   └── src/
+│       ├── components/        # UI, nodes, workflows
+│       ├── routes/            # TanStack Router pages
+│       ├── stores/            # Zustand state (editor.ts)
+│       └── queries/           # React Query definitions
+├── pyproject.toml             # Python config + Ruff settings
+└── .pre-commit-config.yaml    # Pre-commit hooks
+```
+
+## Commands
+
+```bash
+# Tests
+bench --site test_site run-tests --app hazelnode
+
+# Frontend dev
+cd frontend && npm run dev      # Port 8080
+cd frontend && npm run build    # Build to ../hazelnode/public/frontend/
+
+# Linting
+ruff check .                    # Python lint
+ruff format .                   # Python format
+cd frontend && npm run lint     # TypeScript lint
+```
+
+## Code Style
+
+**Python:** Ruff formatter/linter. Line length 70, tabs, single quotes.
+**TypeScript:** ESLint + Prettier. Strict mode enabled.
+
+Pre-commit hooks auto-run on commit (ruff format, ruff check, import sorting).
+
+## Architecture
+
+### Workflow Execution
+- Graph-based execution with context passing between nodes
+- Triggers: Schedule (CRON), Document Event, Webhook
+- Actions: Email, API Call, Condition, Create/Update Doc, Set Variable, Log, Delay
+- Condition nodes return `{branch: 'true'|'false'}` for branching
+
+### Key Doctypes
+- `Hazel Workflow` - Workflow definition with nodes/connections
+- `Hazel Node` - Individual node config
+- `Hazel Node Type` - Node type definitions (fixtures)
+- `Hazel Workflow Execution Log` - Execution history
+
+### Frontend State
+- Editor store (Zustand): nodes, edges, flow state
+- React Query: server state for workflows/users
+- ReactFlow: visual workflow editor
+
+## Key Files
+
+| File | Purpose |
+|------|---------|
+| `hazelnode/hazelnode/doctype/hazel_workflow/hazel_workflow.py` | Workflow execution logic |
+| `hazelnode/nodes/__init__.py` | Abstract Node base class |
+| `hazelnode/nodes/triggers/hazel_webhook_handler.py` | Webhook handler |
+| `hazelnode/hooks.py` | Frappe hooks, fixtures, routing |
+| `frontend/src/stores/editor.ts` | Zustand editor state |
+| `frontend/src/routes/workflow.$id.tsx` | Workflow editor page |
+
+## Conventions
+
+- Node IDs: `node_${counter}_${timestamp}`
+- Template vars in params: `{{ variable_name }}`
+- API endpoints: `@frappe.whitelist()` decorator
+- Error handling: `frappe.throw()` for user errors
+- Frontend basepath: `/hazelnode`
+
+## CI/CD
+
+- Triggers on `develop` branch push and all PRs
+- Services: MariaDB 10.6, Redis (ports 13000, 11000)
+- Python 3.14, Node 24
+- Runs: `bench --site test_site run-tests --app hazelnode`