feat(tty): initialize alknet-tty crate skeleton

Create crates/alknet-tty with Cargo.toml (alknet-core path dep, tokio,
bytes, futures-core, tokio-stream, serde, serde_json, async-trait,
tracing, thiserror — no portable_pty/bollard/russh/alknet-call per
ADR-057), the `local` feature gate (dep wiring deferred to
tty/local-feature-reexport), src/lib.rs with the crate doc comment and
module declarations, and skeleton modules (wire, control, negotiation,
backend, adapter) with doc comments and TODO markers. Add the crate to
the workspace members list.

cargo check, clippy -D warnings, and fmt --check all pass.

Cargo.toml

@@ -4,6 +4,7 @@ members = [
     "crates/alknet-core",
     "crates/alknet-call",
     "crates/alknet-http",
+    "crates/alknet-tty",
 ]
 resolver = "2"