Add CLAUDE.md documentation

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is the volsync-addon-controller, an addon controller for Red Hat Advanced Cluster Management (ACM). It deploys the VolSync operator on managed clusters when ManagedClusterAddOn CRs are created.
+
+## Development Commands
+
+### Building and Testing
+
+```bash
+# Run all tests with coverage
+make test
+
+# Run linting
+make lint
+
+# Build the controller binary
+make build
+
+# Build Docker image
+make docker-build
+
+# Run the controller locally pointing to a remote cluster
+make run
+```
+
+### Key Test Commands
+
+- `make test` - Runs the full test suite using Ginkgo with coverage reporting
+- Test files follow the `*_test.go` pattern and use Ginkgo/Gomega testing framework
+- Tests are located in the `controllers/` directory alongside the main code
+
+### Go Environment
+
+- Go version: 1.24.4 (see go.mod)
+- Uses golangci-lint for code quality checks
+- Configuration in `.golangci.yml` with additional linters enabled
+
+## Architecture
+
+### Core Components
+
+1. **Main Controller** (`controllers/addoncontroller.go`)
+   - Uses the Open Cluster Management addon framework
+   - Implements the `volsyncAgent` that manages VolSync deployments
+   - Deploys VolSync via Helm charts (ACM 2.13+) or OLM subscriptions (legacy)
+
+2. **Label-based Installation** (`controllers/addon_installbylabel_controller.go`)
+   - Monitors ManagedCluster resources for the label `addons.open-cluster-management.io/volsync="true"`
+   - Automatically creates ManagedClusterAddOn resources when the label is present
+
+3. **Manifest Helpers**
+   - `manifesthelper_helmdeploy.go` - Handles Helm-based deployments (current approach)
+   - `manifesthelper_operatordeploy.go` - Handles OLM subscription deployments (legacy)
+
+4. **Helm Utilities** (`controllers/helmutils/`)
+   - Manages embedded Helm charts for VolSync deployment
+   - Handles chart templating and customization
+
+### Deployment Modes
+
+- **Modern (ACM 2.13+)**: Deploys VolSync as a Helm chart on managed clusters
+- **Legacy (ACM 2.12-)**: Deploys VolSync as an OpenShift operator via OLM subscription
+
+### Key Directories
+
+- `controllers/` - Main controller logic and tests
+- `controllers/helmutils/` - Helm chart management utilities
+- `controllers/manifests/` - YAML manifests for deployments
+- `helmcharts/` - Embedded Helm charts for VolSync
+- `hack/` - Development and testing utilities
+
+### Integration Points
+
+- Open Cluster Management addon framework for managed cluster integration
+- Kubernetes controller-runtime for controller implementation
+- Helm v3 for chart management and deployment
+- ACM's MultiClusterHub (MCH) for default image configurations
+
+## Local Development
+
+When running locally with `make run`, the controller:
+- Runs in the `open-cluster-management` namespace
+- Uses embedded charts from the local `helmcharts/` directory
+- Requires KUBECONFIG to be set for cluster access
+- Loads default VolSync images from ACM's MCH image-manifest configmap