fix(gateway): add Python validator coordination API shims

Legacy agents call /v1/validators/register and related routes against
chain.joinbase.ai; the Rust gateway never exposed them, causing 404s.
Add in-memory compat routes so old validators can register, heartbeat,
and fetch registry/weights without challenge-assignment work.

Author: echobt

Cargo.lock

@@ -0,0 +1,30 @@
+[package]
+name = "gateway-compat"
+description = "Legacy Python validator coordination shims for the Rust gateway"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+rust-version.workspace = true
+publish = false
+
+[dependencies]
+axum = { version = "0.8", default-features = false, features = ["http1", "tokio", "json"] }
+hex = "0.4"
+keystore = { path = "../keystore" }
+parking_lot = "0.12"
+schnorrkel = { version = "0.11.5", default-features = false, features = ["std"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+sha2 = "0.10"
+trustroot = { path = "../trustroot" }
+
+[dev-dependencies]
+tokio = { version = "1", features = ["macros", "rt-multi-thread"] }
+tower = { version = "0.5", features = ["util"] }
+http-body-util = "0.1"
+schnorrkel = { version = "0.11.5", default-features = false, features = ["std", "getrandom"] }
+rand_core = { version = "0.6", features = ["getrandom"] }
+
+[lints]
+workspace = true