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

hooks/mod.rs

@@ -0,0 +1,16 @@
+//! Git hooks management for GitKS.
+//!
+//! Supports three layers of hooks:
+//! 1. Server hooks: admin-level, shared across all repositories
+//! 2. Custom hooks: per-repository, user-defined scripts
+//! 3. gRPC callback hooks: external HookService via gRPC
+//!
+//! Hook scripts are installed into bare repositories' `hooks/` directory
+//! and are automatically invoked by git during receive-pack operations.
+
+pub mod manager;
+pub mod runner;
+pub mod sanitize;
+
+pub use manager::HookManager;
+pub use runner::HookResult;