add gatunad server and winforms client v1 (TCP-only)

Raw-Ethernet tunnel over ethertype 0x6969 to bypass WFP killswitches.
Server (Rust, AF_PACKET + classic BPF) relays TCP to 127.0.0.1 services.
Client (.NET 8 WinForms, SharpPcap/Npcap) discovers upstreams and exposes
local loopback listeners. Wire protocol: 6-byte header, 7 frame types,
MANIFEST with labeled upstreams. UDP types reserved, unimplemented.

gatunad/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "gatuna"
+version = "0.1.0"
+edition = "2021"
+license = "CC0-1.0"
+
+[[bin]]
+name = "gatunad"
+path = "src/main.rs"
+
+[dependencies]
+libc = "0.2"
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "net", "sync", "io-util"] }
+clap = { version = "4", features = ["derive"] }
+pnet_datalink = "0.35"
+tracing = "0.1"
+tracing-subscriber = "0.3"