refactor: rename the backend to dsh-subagent-dsh-sdk

The group's convention is package suffix == provider default
(subagent-acp/'acp', subagent-spawn/'spawn', subagent-fork/'fork'), and the
provider default became dsh-sdk in the last review round — so the package
follows: @deepseek-ai/dsh-subagent-dsh-sdk at
packages/subagent/subagent-dsh-sdk, plugin name subagent-dsh-sdk,
diagnostics prefixed subagent-dsh-sdk:. The dsh echo has precedent
(dsh-llm-deepseek). Directory, fixture path, knip/tsconfig/examples
registrations, catalogs, READMEs (en+zh), and the Agent Note follow; the
sdk-client dispose ladder moves to its own module (src/dispose.ts) with the
deterministic FakeChild tier tests restored alongside it.

examples/jsonrpc-agent/tests/fixtures/subagent/subagent-dsh-sdk/driver.ts

@@ -0,0 +1,15 @@
+#!/usr/bin/env node
+/** Test driver: one delegation turn through a headless Loader composition. */
+
+import { boot, resolveConfigPath } from '@deepseek-ai/dsh-app-boot'
+import { runOneShot } from '@deepseek-ai/dsh-cli-demo/src/cli.ts'
+
+const configPath = process.argv[2]
+if (configPath === undefined) throw new Error('sdk-subagent cwd driver requires a config path')
+
+const ctx = await boot('sdk-subagent-cwd-e2e', resolveConfigPath(configPath, undefined))
+try {
+  await runOneShot(ctx, { task: 'delegate' })
+} finally {
+  await ctx.fiber.dispose()
+}