Implement Phase 1 of KAT (#1)

**Phase 1: State Management & Leader Election**
*   **Goal**: A functional embedded etcd and leader election mechanism.
*   **Tasks**:
    1.  Implement the `StateStore` interface (RFC 5.1) with an etcd backend (`internal/store/etcd.go`).
    2.  Integrate embedded etcd server into `kat-agent` (RFC 2.2, 5.2), configurable via `cluster.kat` parameters.
    3.  Implement leader election using `go.etcd.io/etcd/client/v3/concurrency` (RFC 5.3).
    4.  Basic `kat-agent init` functionality:
        *   Parse `cluster.kat`.
        *   Start single-node embedded etcd.
        *   Campaign for and become leader.
        *   Store initial cluster configuration (UID, CIDRs from `cluster.kat`) in etcd.
*   **Milestone**:
    *   A single `kat-agent init --config cluster.kat` process starts, initializes etcd, and logs that it has become the leader.
    *   The cluster configuration from `cluster.kat` can be verified in etcd using an etcd client.
    *   `StateStore` interface methods (`Put`, `Get`, `Delete`, `List`) are testable against the embedded etcd.

Reviewed-on: #1

internal/testutil/testutil.go

@@ -0,0 +1,85 @@
+package testutil
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"git.dws.rip/dubey/kat/internal/store"
+	"github.com/stretchr/testify/require"
+	"go.etcd.io/etcd/server/v3/embed"
+)
+
+// SetupEmbeddedEtcd creates a temporary directory and starts an embedded etcd server for testing
+func SetupEmbeddedEtcd(t *testing.T) (string, *embed.Etcd, string) {
+	// Create a temporary directory for etcd data
+	tempDir, err := os.MkdirTemp("", "etcd-test-*")
+	require.NoError(t, err)
+
+	// Configure and start embedded etcd
+	etcdConfig := store.EtcdEmbedConfig{
+		Name:           "test-node",
+		DataDir:        tempDir,
+		ClientURLs:     []string{"http://localhost:0"}, // Use port 0 to get a random available port
+		PeerURLs:       []string{"http://localhost:0"},
+		InitialCluster: "test-node=http://localhost:0",
+	}
+
+	etcdServer, err := store.StartEmbeddedEtcd(etcdConfig)
+	require.NoError(t, err)
+
+	// Get the actual client URL that was assigned
+	clientURL := etcdServer.Clients[0].Addr().String()
+
+	return tempDir, etcdServer, clientURL
+}
+
+// CreateTestClusterConfig creates a test cluster.kat file in the specified directory
+func CreateTestClusterConfig(t *testing.T, dir string) string {
+	configContent := `apiVersion: kat.dws.rip/v1alpha1
+kind: ClusterConfiguration
+metadata:
+  name: test-cluster
+spec:
+  clusterCidr: "10.100.0.0/16"
+  serviceCidr: "10.101.0.0/16"
+  nodeSubnetBits: 7
+  clusterDomain: "test.cluster.local"
+  agentPort: 9116
+  apiPort: 9115
+  etcdPeerPort: 2380
+  etcdClientPort: 2379
+  volumeBasePath: "/var/lib/kat/volumes"
+  backupPath: "/var/lib/kat/backups"
+  backupIntervalMinutes: 30
+  agentTickSeconds: 15
+  nodeLossTimeoutSeconds: 60
+`
+	configPath := filepath.Join(dir, "cluster.kat")
+	err := os.WriteFile(configPath, []byte(configContent), 0644)
+	require.NoError(t, err)
+	return configPath
+}
+
+// WaitForCondition waits for the given condition function to return true or times out
+func WaitForCondition(t *testing.T, condition func() bool, timeout time.Duration, message string) {
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+
+	ticker := time.NewTicker(50 * time.Millisecond)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			require.Fail(t, "Timed out waiting for condition: "+message)
+			return
+		case <-ticker.C:
+			if condition() {
+				return
+			}
+		}
+	}
+}