refactor(actor): implement replica sync and ref update notification system

- Add is_write parameter to remote clients for read/write routing distinction
- Introduce RepoEntry struct with role tracking (primary/replica) for repositories
- Replace HashSet with HashMap for repository storage with role metadata
- Add ROLE_PRIMARY and ROLE_REPLICA constants for node role identification
- Implement FindPrimary and FindReplica RPC methods for role-based routing
- Add RefUpdateEvent message type for propagating reference updates
- Create sync module with BundleApplicator for handling replica synchronization
- Implement notify_ref_update calls after branch/tag/commit operations
- Add broadcast_ref_update function to propagate events across cluster nodes
- Modify route_repository to prioritize primary for writes and replicas for reads
- Update actor message handling to support role-based repository discovery
- Implement sync_from_primary function using pack protocol for incremental updates

actor/mod.rs

@@ -1,7 +1,8 @@
 pub mod message;
 pub mod handler;
 pub mod server;
+pub mod sync;
 
-pub use handler::{GitNodeActor, GitNodeArgs, start_node_actor, get_cluster_nodes, get_category_members, route_group_for, list_all_groups};
+pub use handler::{GitNodeActor, GitNodeArgs, RepoEntry, start_node_actor, get_cluster_nodes, get_category_members, route_group_for, list_all_groups, broadcast_ref_update};
 pub use server::init_actor_cluster;
-pub use message::{GitNodeMessage, NodeHealth, RepoActorMessage, RouteDecision};
+pub use message::{GitNodeMessage, NodeHealth, RefUpdateEvent, RepoActorMessage, RouteDecision, ROLE_PRIMARY, ROLE_REPLICA};