feat(client): add TAP-Windows adapter crate

The Windows client still needs a real Ethernet TAP boundary before it can pump
frames between the adapter and the relay session. Keep that OS-specific surface
separate from the QUIC client state by adding a `lanparty-client-tap` crate.

The new crate discovers TAP-Windows6 adapters through the Windows network
adapter registry class, validates `tap0901` component ids, constructs the
`\\.\Global\{NetCfgInstanceId}.tap` device path, opens the TAP device handle,
and exposes blocking Ethernet frame read/write helpers. It also wraps the
TAP-Windows IOCTLs for media status, driver MAC, and driver MTU.

This does not wire the TAP crate into `lanparty-client-win` yet and does not
attempt route protection. The value of this slice is the target-checkable OS
boundary that the next client pump can depend on.

Test Plan:
- cargo fmt --check
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings
- Windows-target cargo check for lanparty-client-tap with clang-cl/lld-link
- Windows-target cargo clippy for lanparty-client-tap with -D warnings
- git diff --check

Refs: PLAN.md Windows TAP client

Cargo.toml

@@ -2,6 +2,7 @@
 resolver = "3"
 members = [
   "crates/lanparty-client-core",
+  "crates/lanparty-client-tap",
   "crates/lanparty-client-win",
   "crates/lanparty-ctrl",
   "crates/lanparty-gateway",
@@ -28,3 +29,4 @@ serde_json = "1"
 thiserror = "2"
 tokio = { version = "1.52.3", features = ["macros", "net", "rt-multi-thread", "signal", "sync", "time"] }
 tracing = "0.1"
+windows-sys = "0.61.2"