feat(cluster): implement distributed clustering with etcd coordination

- Integrate etcd-client for distributed coordination and leader election
- Add remote client macros with proper formatting for all services
- Implement RequestMetrics for tracking RPC performance and errors
- Add rate limiting mechanism across all service endpoints
- Create ElectionRequest and ElectionResult message types for leader election
- Add role management with primary/replica switching capabilities
- Implement health checker with automatic failover detection
- Add repository count metrics for cluster monitoring
- Update Cargo.toml with etcd-client and dashmap dependencies
- Modify RepoEntry to include read_only flag for replica handling
- Implement should_accept_election logic to prevent duplicate elections
- Add RoleChangedEvent handling for cluster role updates

actor/mod.rs

@@ -4,11 +4,11 @@ pub mod server;
 pub mod sync;
 
 pub use handler::{
-    GitNodeActor, GitNodeArgs, RepoEntry, broadcast_ref_update, get_category_members,
-    get_cluster_nodes, list_all_groups, route_group_for, start_node_actor,
+    GitNodeActor, GitNodeArgs, RepoEntry, broadcast_ref_update, broadcast_role_changed,
+    get_category_members, get_cluster_nodes, list_all_groups, route_group_for, start_node_actor,
 };
 pub use message::{
-    GitNodeMessage, NodeHealth, ROLE_PRIMARY, ROLE_REPLICA, RefUpdateEvent, RepoActorMessage,
-    RouteDecision,
+    ElectionRequest, ElectionResult, GitNodeMessage, NodeHealth, ROLE_PRIMARY, ROLE_REPLICA,
+    RefUpdateEvent, RepoActorMessage, RoleChangedEvent, RouteDecision,
 };
 pub use server::init_actor_cluster;