feat(config): integrate etcd for service discovery and config management

- Add etcd-client dependency for distributed configuration storage
- Implement EtcdConfig with priority: etcd > environment variables > defaults
- Add ServiceRegistry for service registration with lease keep-alive
- Integrate etcd-based service discovery for appks gRPC connections
- Add service watcher for real-time service instance updates
- Migrate Redis configuration from single URL to cluster node list
- Update Dockerfile with default IMKS_HOST and IMKS_PORT environment variables
- Add etcd bootstrap configuration through environment variables
- Implement Redis cluster URL building with optional authentication

socket/message_bus/redis.rs

@@ -12,14 +12,17 @@ pub struct RedisMessageBus {
 }
 
 impl RedisMessageBus {
-    pub async fn new(redis_url: &str) -> Result<Self, MessageBusError> {
+    /// Connect to a Redis cluster.
+    ///
+    /// `cluster_url` should be in `redis-cluster://` format, e.g.:
+    /// `redis-cluster://host1:6379,host2:6379,host3:6379`
+    pub async fn new(cluster_url: &str) -> Result<Self, MessageBusError> {
         let config =
-            Config::from_url(redis_url).map_err(|e| MessageBusError::Redis(e.to_string()))?;
+            Config::from_url(cluster_url).map_err(|e| MessageBusError::Redis(e.to_string()))?;
 
         let client = Client::new(config.clone(), None, None, None);
         let subscriber = SubscriberClient::new(config, None, None, None);
 
-        // connect() starts the connection task; result is checked by wait_for_connect()
         let _ = client.connect().await;
         let _ = subscriber.connect().await;
 
@@ -32,6 +35,7 @@ impl RedisMessageBus {
             .await
             .map_err(|e| MessageBusError::Redis(e.to_string()))?;
 
+        tracing::info!(cluster_url, "Redis cluster connected");
         Ok(Self { client, subscriber })
     }