**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
