fix: complete rewrite of all client source files for clean compilation

- Rewrite noise.rs with correct snow 0.9 Builder API (was using non-existent types)
- Add noise.rs to git tracking (root cause of persistent E0583)
- Remove old src/noise.rs from repo root (was in wrong location)
- Fix tun.rs: restore std::io::{Read, Write} imports, rename methods to avoid conflict
- Fix coordinator_client.rs: use GrpcCoordinatorClient to avoid naming collision
- Fix main.rs: rename mock gRPC module to coordinator::grpc, add mock method impls
- Fix transport.rs: use send_to() instead of send(), avoid self borrow in spawned task
- Add tokio net/sync/time features to Cargo.toml

Co-Authored-By: Claude Code <noreply@anthropic.com>

client/Cargo.toml

@@ -4,7 +4,7 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-tokio = { version = "1", features = ["rt", "macros", "rt-multi-thread"] }
+tokio = { version = "1", features = ["rt", "macros", "rt-multi-thread", "net", "sync", "time"] }
 bytes = "1"
 tonic = "0.12"
 prost = "0.13"