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/client/package.json

@@ -5,6 +5,16 @@
   "type": "module",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
+    },
+    "./rpc/contract": {
+      "types": "./dist/rpc/contract.d.ts",
+      "import": "./dist/rpc/contract.js"
+    }
+  },
   "scripts": {
     "build": "bunx --bun tsc",
     "dev": "tsc --watch",