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/lib.rs

@@ -0,0 +1,10 @@
+//! alknet-call: Structured RPC over QUIC — operations, streaming, service discovery.
+//!
+//! Implements [`alknet_core::types::ProtocolHandler`] on ALPN `alknet/call`.
+//!
+//! The crate has two subsystems:
+//! - [`registry`] — operation specs, context, dispatch, and the operation registry.
+//! - [`protocol`] — wire format, streams, and the call adapter.
+
+pub mod protocol;
+pub mod registry;