feat(sdk): TypeScript SDK client + shared wire protocol + SDK subagent backend

- @deepseek-ai/dsh-sdk-protocol: extract the line transport from dsh-jsonrpc
  and name the request/result/notification wire types both ends share; error
  responses preserve wire code/data via JsonRpcResponseError.
- @deepseek-ai/dsh-sdk-client: TypeScript twin of the Python SDK — spawns the
  dsh-jsonrpc-agent runtime as a subprocess, drives stdio JSON-RPC turns
  (DeepSeekHarness high-level API + HarnessClient protocol client), scopes
  notifications to session trees client-side, and reaps the child through the
  shared subprocess dispose ladder.
- @deepseek-ai/dsh-subagent-sdk: out-of-process subagent backend driving a
  child harness runtime through the TS SDK; shares cwd resolution with
  subagent-acp via new dsh-subagent-subprocess cwd helpers.
- Keyless unit suites drive real subprocesses (scripted fake runtime peer);
  100% per-file coverage on all touched packages.

packages/sdk/sdk-protocol/src/index.ts

@@ -0,0 +1,12 @@
+/**
+ * Shared wire protocol for the DeepSeek Harness SDK runtime: the
+ * newline-delimited JSON-RPC stdio transport plus the named request, result,
+ * and notification types both wire ends speak. The runtime server plugin
+ * (`@deepseek-ai/dsh-jsonrpc`) serves this protocol; SDK clients
+ * (`@deepseek-ai/dsh-sdk-client`, the Python SDK) drive it.
+ *
+ * @module @deepseek-ai/dsh-sdk-protocol
+ */
+
+export * from './transport.ts'
+export * from './types.ts'