docs(arch): extract AlknetEndpoint into alknet-endpoint (ADR-083 Am. 2026-07-15)

Amend ADR-083 with the crate-extraction decision: the endpoint moves
from alknet-core into a new crate alknet-endpoint, mirroring the
alknet-client extraction (ADR-089). The ADR's shape (new + builder
methods + public dispatch + run/shutdown) is unchanged; only the
location changes.

The extraction is structural pruning, not an inline refactor. The
endpoint is a leaf consumer of core's shared types (zero handler crates
import it; 124 import sites for the other core modules). Extracting it
lets core shed quinn/iroh/rcgen/rustls-acme — handler crates no longer
transitively link those. A pure worker (client-only) does not pull
alknet-endpoint at all. The dep graph is symmetric: alknet-core is the
shared types crate; alknet-endpoint and alknet-client are the
server-side and client-side establishment crates.

New spec: crates/endpoint/README.md (the canonical endpoint spec).
core/endpoint.md is deprecated to a stub. Cross-references updated
across 8 docs (README, overview, tls, hub, client, core README, ADR-083,
ADR-089 references). Architecture review passed (3 critical, 9 warnings
— all addressed).

docs/architecture/crates/hub/README.md

@@ -657,15 +657,18 @@ alknet-hub (Hub struct deps)
 │                from_call, FromCallConfig, AdapterError, ClientError)
 ├── alknet-http (HttpAdapter — for the registration endpoint and browser access)
 ├── alknet-core (IdentityProvider, Connection, OperationRegistry,
-│                HandlerRegistry, AuthContext)
+│                AuthContext)
 ├── tokio (spawn, time::sleep)
 └── tracing (logging)
 
   (assembly-layer deps — used by the hub's composition code, not by
    the Hub struct itself)
+  ├── alknet-endpoint (AlknetEndpoint with quinn + iroh + tcp features,
+  │   │               HandlerRegistry — the accept-loop runner)
+  ├── alknet-client (AlknetClient — outbound worker dials, ADR-089)
   ├── alknet-tls (TlsServerConfig — builds the raw-key + X.509/ACME
   │               configs handed to the endpoint's transports)
-  └── alknet-core [tcp feature] (with_tcp_tls — the TCP+TLS accept loop)
+  └── alknet-core [quinn/iroh features] (Connection::from_quinn/from_iroh)
 ```
 
 `alknet-hub` depends on `alknet-channels-call`, `alknet-call`, and