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/apiproxy/tsconfig.json

@@ -55,6 +55,9 @@
     },
     {
       "path": "../../support/invariants"
+    },
+    {
+      "path": "../../util/native-command"
     }
   ]
 }