refactor(ts): complete legacy host removal — drop fastify/commander/zod, delete MCP SDK server, remove ManagedRuntime facades

Finishes the remaining EFFECT_NATIVE_REWRITE_PLAN stages in one verified slice:
- fastify, @fastify/websocket, commander, zod removed from all package manifests
- legacy @modelcontextprotocol/sdk stdio server deleted; effect/unstable/ai McpServer is canonical
- no ManagedRuntime or Effect.runPromise program facades remain in production source
- gateway server/rpc-contract and client rpc/socket moved onto Effect v4 native http/rpc/socket layers

Gates (force-run, no cache): check:tsgo, build, test (96 tests / 11 tasks) all green.
Native-class inventory: zero blocking production classes.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ts/packages/flow/src/gateway/dispatch/manager.ts

@@ -12,6 +12,7 @@ import { Clock, Effect, Exit, HashMap, HashSet, Option, Random, Scope, Synchroni
 import {
   loadMessagingRuntimeConfig,
   makeNatsBackend,
+  makeNatsBackendScoped,
   makePubSubService,
   makeRequestResponseFactoryService,
   messagingDeliveryError,
@@ -401,3 +402,17 @@ export function makeDispatcherManager(config: GatewayConfig): DispatcherManager
     publishToTopic,
   };
 }
+
+export const makeDispatcherManagerScoped = Effect.fn("makeDispatcherManagerScoped")(function* (
+  config: GatewayConfig,
+) {
+  if (config.pubsub !== undefined) {
+    return makeDispatcherManager(config);
+  }
+
+  const pubsub = yield* makeNatsBackendScoped(config.natsUrl ?? "nats://localhost:4222");
+  return makeDispatcherManager({
+    ...config,
+    pubsub,
+  });
+});