feat(call,http): expose EventEnvelope-level dispatch API for non-QUIC transports

Make Dispatcher::dispatch_requested pub and extract abort-cascade handling
into a pub handle_abort method so the WebSocket handler can feed deserialized
EventEnvelopes directly to the shared Dispatcher without a QUIC Connection.

CallConnection gains a new_overlay_only(identity) constructor (Option A) that
holds the Layer 2 overlay, PendingRequestMap, and resolved bearer Identity
without a QUIC Connection; identity() reads the stored field for the non-QUIC
case. compose_root_env uses the new identity() accessor for both paths.

The existing QUIC path (CallAdapter, CallClient, run_loop, handle_stream) is
unchanged — outgoing client methods guard on connection().is_none().

crates/alknet-call/src/client/call_client.rs

@@ -708,7 +708,10 @@ mod tests {
         let registry = registry_with_caps();
         let client = CallClient::new(Arc::clone(&registry), Arc::new(NoopIdentityProvider));
         let conn = client.spawn_dispatch(stub_connection());
-        assert_eq!(conn.connection().remote_alpn(), b"alknet/call");
+        assert_eq!(
+            conn.connection().expect("quic connection present").remote_alpn(),
+            b"alknet/call"
+        );
         std::mem::drop(conn);
     }