fix: point node-mode launcher at the renamed dsh-jsonrpc-demo package

_node_launch_args builds the launcher path from segments, so the package
rename to dsh-jsonrpc-demo did not reach it via the path sweep. A freshly
deployed node closure ships @deepseek-ai/dsh-jsonrpc-demo, so node mode
raised FileNotFoundError. The docstring and exe ENTRY_BIN already use the
new name.

python/sdk-runtime/src/deepseek_harness_runtime/__init__.py

@@ -123,7 +123,7 @@ def _current_platform_tag() -> str:
 def _node_launch_args() -> tuple[str, str]:
     node_root = bundled_package_dir() / "runtime" / "node"
     bin_js = (
-        node_root / "node_modules" / "@deepseek-ai" / "dsh-jsonrpc-agent" / "lib" / "bin.js"
+        node_root / "node_modules" / "@deepseek-ai" / "dsh-jsonrpc-demo" / "lib" / "bin.js"
     )
     if not bin_js.is_file():
         raise FileNotFoundError(