feat: add @claudemesh/sdk standalone client library

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/sdk/src/index.ts

@@ -0,0 +1,9 @@
+export { MeshClient } from "./client.js";
+export { generateKeyPair } from "./crypto.js";
+export type {
+  PeerInfo,
+  InboundMessage,
+  Priority,
+  ConnStatus,
+  MeshClientOptions,
+} from "./types.js";