refactor!: rebrand wraith to alknet

Rename all crates, CLI commands, constants, type names, doc comments,
and documentation from wraith to alknet. Includes wire-protocol changes:
ALPN wraith-ssh -> alknet-ssh, reserved destination prefix wraith- ->
alknet-, SSH auth username wraith -> alknet.

crates/alknet-core/tests/server_tests.rs

@@ -0,0 +1,2 @@
+#[tokio::test]
+async fn server_placeholder() {}