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/registry/mod.rs

@@ -0,0 +1,12 @@
+//! Operation registry: specs, handlers, access control, service discovery.
+//!
+//! Maps operation names to specs and handlers, enforces access control, and
+//! dispatches `call.requested` events to local handlers. The registry is
+//! layered by trust boundary (ADR-024): a curated layer (immutable after
+//! startup) plus dynamic session and connection overlays.
+
+pub mod context;
+pub mod discovery;
+pub mod env;
+pub mod registration;
+pub mod spec;