Add CLAUDE.md file (#3489)

## Why
<!-- Why are these changes needed? Provide the context that the reviewer
might be missing.
For example, were there any decisions behind the change that are not
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Following best practices listed
[here](https://www.anthropic.com/engineering/claude-code-best-practices):
- ran /init
- made some small changes to the initial content

Author: anton-107

CLAUDE.md

@@ -0,0 +1,89 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is the Databricks CLI, a command-line interface for interacting with Databricks workspaces and managing Databricks Assets Bundles (DABs). The project is written in Go and follows a modular architecture.
+
+## Development Commands
+
+### Building and Testing
+- `make build` - Build the CLI binary
+- `make test` - Run unit tests for all packages
+- `go test ./acceptance -run TestAccept/bundle/<path>/<to>/<folder> -tail -test.v` - run a single acceptance test
+- `make integration` - Run integration tests (requires environment variables)
+- `make cover` - Generate test coverage reports
+
+### Code Quality
+- `make lint` - Run linter on changed files only (uses lintdiff.py)
+- `make lintfull` - Run full linter with fixes (golangci-lint)
+- `make ws` - Run whitespace linter
+- `make fmt` - Format code (Go, Python, YAML)
+- `make checks` - Run quick checks (tidy, whitespace, links)
+
+### Specialized Commands
+- `make schema` - Generate bundle JSON schema
+- `make docs` - Generate bundle documentation
+- `make generate` - Generate CLI code from OpenAPI spec (requires universe repo)
+
+## Architecture
+
+### Core Components
+
+**cmd/** - CLI command structure using Cobra framework
+- `cmd/cmd.go` - Main command setup and subcommand registration
+- `cmd/bundle/` - Bundle-related commands (deploy, validate, etc.)
+- `cmd/workspace/` - Workspace API commands (auto-generated)
+- `cmd/account/` - Account-level API commands (auto-generated)
+
+**bundle/** - Core bundle functionality for Databricks Asset Bundles
+- `bundle/bundle.go` - Main Bundle struct and lifecycle management
+- `bundle/config/` - Configuration loading, validation, and schema
+- `bundle/deploy/` - Deployment logic (Terraform and direct modes)
+- `bundle/mutator/` - Configuration transformation pipeline
+- `bundle/phases/` - High-level deployment phases
+
+**libs/** - Shared libraries and utilities
+- `libs/dyn/` - Dynamic configuration value manipulation
+- `libs/filer/` - File system abstraction (local, DBFS, workspace)
+- `libs/auth/` - Databricks authentication handling
+- `libs/sync/` - File synchronization between local and remote
+
+### Key Concepts
+
+**Bundles**: Configuration-driven deployments of Databricks resources (jobs, pipelines, etc.). The bundle system uses a mutator pattern where each transformation is a separate, testable component.
+
+**Mutators**: Transform bundle configuration through a pipeline. Located in `bundle/config/mutator/` and `bundle/mutator/`. Each mutator implements the `Mutator` interface.
+
+**Direct vs Terraform Deployment**: The CLI supports two deployment modes controlled by `DATABRICKS_CLI_DEPLOYMENT` environment variable:
+- `terraform` (default) - Uses Terraform for resource management
+- `direct` - Direct API calls without Terraform
+
+## Testing
+
+### Test Types
+- **Unit tests**: Standard Go tests alongside source files
+- **Integration tests**: `integration/` directory, requires live Databricks workspace
+- **Acceptance tests**: `acceptance/` directory, uses mock HTTP server
+
+### Acceptance Tests
+- Located in `acceptance/` with nested directory structure
+- Each test directory contains `databricks.yml`, `script`, and `output.txt`
+- Run with `go test ./acceptance -run TestAccept/bundle/<path>/<to>/<folder> -tail -test.v`
+- Use `-update` flag to regenerate expected output files
+- When you see the test fails because it has an old output, just run it one more time with an `-update` flag instead of changing the `output.txt` directly
+
+## Code Patterns
+
+### Configuration
+- Bundle config uses `dyn.Value` for dynamic typing
+- Config loading supports includes, variable interpolation, and target overrides
+- Schema generation is automated from Go struct tags
+
+## Development Tips
+
+- Run `make checks fmt lint` before committing
+- Use `make test-update` to regenerate acceptance test outputs after changes
+- The CLI binary supports both `databricks` and `pipelines` command modes based on executable name
+- Resource definitions in `bundle/config/resources/` are auto-generated from OpenAPI specs