refactor(util): extract the shared no-shell native-command runner to dsh-native-command

master's toolcall-open extracted runNativeCommand inside apiproxy for the
openPath opener while the picker seam had moved the native chooser (its other
consumer) into directory-picker-native; after the merge the two packages each
carried a verbatim copy. The runner now lives in packages/util/native-command
(zero-dependency library, per the util-group contract) and both native
integrations depend on it.

packages/host/directory-picker-native/package.json

@@ -27,7 +27,8 @@
   ],
   "license": "BSD-3-Clause",
   "dependencies": {
-    "@deepseek-ai/dsh-host-directory-picker": "workspace:^"
+    "@deepseek-ai/dsh-host-directory-picker": "workspace:^",
+    "@deepseek-ai/dsh-native-command": "workspace:^"
   },
   "peerDependencies": {
     "@deepseek-ai/dsh-invariants": "^0.0.1",