feat: extract alknet-call into alkcall, vendor core types

Phase 1 of the alknet-call + alknet-channels unification. The call crate
is extracted verbatim from /workspace/@alkdev/alknet/crates/alknet-call
and the needed alknet-core types are vendored into src/core/ — alkcall is
the home for these types going forward (no separate alkcore crate).

Vendored core types (src/core/):
- auth.rs: Identity, AuthToken, AuthContext, IdentityProvider
- ownership.rs: OwnershipProvider, OwnershipStore, InMemoryOwnershipStore,
  OwnershipError
- types.rs: ProtocolHandler, Connection, BiStream, BidiStreamSource,
  SendStream, RecvStream, HandlerError, StreamError, Capabilities, Secret,
  IdentityAlreadySet
- Stripped: quinn/iroh/rustls deps, Connection::from_quinn/from_iroh
  (the dial lives in the consumer per ADR-089), config/credentials/
  fingerprint/store modules, ConfigIdentityProvider/IdentityStore

Call crate (src/client, src/protocol, src/registry/):
- Copied verbatim from alknet-call; alknet_core::{auth,types,ownership}
  rebound to crate::core::{auth,types,ownership}
- ALPN strings unchanged (alknet/call — wire-stable per ADR-006)
- No behavioral changes

Verification:
- cargo test: 343 passed (0 failed)
- cargo clippy --all-targets -- -D warnings: clean
- cargo fmt --check: clean
- cargo doc --no-deps: 1 pre-existing broken intra-doc link
  (CallAdapter in dispatch.rs — Phase 2 cleanup)

Next: Phase 2 — channels greenfield implementation + ALPN rename +
architecture doc porting.

src/protocol/mod.rs

@@ -0,0 +1,18 @@
+//! 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 dispatch;
+pub mod pending;
+pub mod wire;
+
+#[cfg(test)]
+mod test_support;
+
+#[cfg(test)]
+pub(crate) use test_support::sink_empty_connection;