docs: add CLAUDE.md file with repo guidance for agentic tools

Add guidance file for Claude Code (claude.ai/code) containing build commands, test
instructions, and code style guidelines to help AI assistants work effectively with
this repository.

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

Co-Authored-By: Claude <[email protected]>

Author: NikolayS

Diff for: CLAUDE.md

@@ -0,0 +1,23 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build/Test/Lint Commands
+- Build all components: `cd engine && make build`
+- Lint code: `cd engine && make lint`
+- Run unit tests: `cd engine && make test`
+- Run integration tests: `cd engine && make test-ci-integration`
+- Run a specific test: `cd engine && GO111MODULE=on go test -v ./path/to/package -run TestName`
+- Run UI: `cd ui && pnpm start:ce` (Community Edition) or `pnpm start:platform`
+
+## Code Style Guidelines
+- Go code follows "Effective Go" and "Go Code Review Comments" guidelines
+- Use present tense and imperative mood in commit messages
+- Limit first commit line to 72 characters
+- All Git commits must be signed
+- Format Go code with `cd engine && make fmt`
+- Use error handling with pkg/errors
+- Follow standard Go import ordering
+- Group similar functions together
+- Error messages should be descriptive and actionable
+- UI uses pnpm for package management