feat(http): implement HttpAdapter (ProtocolHandler for h2/http1.1, axum over QUIC)

Wires the axum Router (gateway endpoints + /healthz + /openapi.json + MCP +
custom routes via extra_routes merge ADR-046) and drives hyper's HTTP/1.1 or
HTTP/2 connection driver over a single QUIC bidirectional stream. The
QUIC-to-hyper bridge wraps the (SendStream, RecvStream) pair as a
TokioIo-compatible duplex and feeds it to hyper-util's auto Builder (which
auto-detects HTTP/1.1 vs HTTP/2). h3 ALPN is not registered (ADR-044).

Route handlers, healthz/decoy logic, openapi.json, the MCP route, and the WS
upgrade handler are wired as 501 Not Implemented placeholders for their
respective tasks. The router state holds Arc<OperationRegistry> +
Arc<dyn IdentityProvider>; the router is built once at construction and
cloned per connection (cheap Arc clone). DecoyConfig defaults to NotFound.

Adds hyper-util dependency (server, service, tokio features).

Cargo.lock

@@ -112,6 +112,7 @@ dependencies = [
  "http",
  "httpdate",
  "hyper",
+ "hyper-util",
  "openapiv3",
  "reqwest 0.13.4",
  "reqwest-middleware",