feat: tunnel-node service + CodeFull.gs (#93)

Standalone Rust/axum HTTP server + Apps Script-side CodeFull.gs for users who want to deploy a remote tunnel node. All new files; no changes to the main Rust crate. This is part 1 of 3 of the full-tunnel feature — it adds scaffolding that users can opt into once the Rust-side Mode::Full lands in #94.

tunnel-node/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "mhrv-tunnel-node"
+version = "0.1.0"
+edition = "2021"
+description = "HTTP tunnel bridge for MasterHttpRelayVPN full mode — bridges HTTP tunnel requests to real TCP connections"
+
+[[bin]]
+name = "tunnel-node"
+path = "src/main.rs"
+
+[dependencies]
+axum = "0.7"
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "net", "time", "io-util", "signal", "sync"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+base64 = "0.22"
+uuid = { version = "1", features = ["v4"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+flate2 = "1"
+
+[profile.release]
+panic = "abort"
+codegen-units = 1
+lto = true
+opt-level = 3
+strip = true