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

snapshot/mod.rs

@@ -0,0 +1,13 @@
+//! Repository snapshot and move operations.
+//!
+//! Supports:
+//! - Creating snapshots (git bundle) of repositories for backup
+//! - Restoring snapshots to new or existing repositories
+//! - Moving repositories between cluster nodes
+//! - Listing and deleting snapshots
+
+pub mod ops;
+pub mod storage;
+
+pub use ops::{create_snapshot, restore_snapshot, verify_snapshot};
+pub use storage::{LocalSnapshotStorage, SnapshotInfo, SnapshotStorageBackend};