feat(call): initialize alknet-call crate skeleton (task: call/crate-init)

Create crates/alknet-call with Cargo.toml, lib.rs, and module skeletons
for the registry (spec, context, registration, env, discovery) and
protocol (wire, pending, connection, adapter, abort) subsystems. Add the
crate to the workspace members list. Depends on alknet-core (workspace
path), irpc (workspace dep), tokio, serde, serde_json, async-trait,
tracing, thiserror, uuid, and futures. Implements ProtocolHandler on
ALPN alknet/call per docs/architecture/crates/call.

crates/alknet-call/src/protocol/mod.rs

@@ -0,0 +1,11 @@
+//! Call protocol: wire format, streams, and the call adapter.
+//!
+//! Implements `ProtocolHandler` for ALPN `alknet/call` on top of the
+//! operation registry. See `docs/architecture/crates/call/call-protocol.md`
+//! for the full specification.
+
+pub mod abort;
+pub mod adapter;
+pub mod connection;
+pub mod pending;
+pub mod wire;