phase 4: connectrpc on the gateway authenticated edge

Replace the native-gRPC server bootstrap with a single
`connectrpc.com/connect` HTTP/h2c listener. Connect-Go natively
serves Connect, gRPC, and gRPC-Web on the same port, so browsers can
now reach the authenticated surface without giving up the gRPC
framing native and desktop clients may use later. The decorator
stack (envelope → session → payload-hash → signature →
freshness/replay → rate-limit → routing/push) is reused unchanged
behind a small Connect → gRPC adapter and a `grpc.ServerStream`
shim around `*connect.ServerStream`.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

gateway/internal/grpcapi/session_lookup.go

@@ -123,7 +123,7 @@ func (unavailableSessionCache) Lookup(context.Context, string) (session.Record,
 	return session.Record{}, errors.New("session cache is unavailable")
 }
 
-func (unavailableSessionCache) MarkRevoked(string)         {}
+func (unavailableSessionCache) MarkRevoked(string)           {}
 func (unavailableSessionCache) MarkAllRevokedForUser(string) {}
 
 var _ gatewayv1.EdgeGatewayServer = sessionLookupService{}