feat(client): add relay CLI for Windows binary

lanparty-client-win now has a real command-line surface for the relay-facing
client session. It accepts the relay address, expected TLS server name, pinned
DER relay certificate, room code, virtual TAP MAC, and advertised datagram
budget, then connects through lanparty-client-core as role = client.

The binary reports the assigned peer id, room id, and effective TAP MTU from the
welcome response, then waits for Ctrl-C. TAP adapter binding and Windows route
pinning remain future slices, but the executable now exercises the real relay
control-plane path instead of the starter placeholder.

Test Plan:
- cargo fmt --check
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings

Refs: PLAN.md Windows client relay connection

Cargo.lock

@@ -446,6 +446,14 @@ dependencies = [
 [[package]]
 name = "lanparty-client-win"
 version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "clap",
+ "lanparty-client-core",
+ "lanparty-ctrl",
+ "lanparty-proto",
+ "tokio",
+]
 
 [[package]]
 name = "lanparty-ctrl"