Plumb local and remote environment selection through threads and thread APIs

Co-authored-by: Codex <noreply@openai.com>

codex-rs/app-server-protocol/schema/json/v2/ThreadStartParams.json

@@ -157,6 +157,13 @@
         "null"
       ]
     },
+    "environmentId": {
+      "description": "Optional environment selection. Use `\"local\"` or `\"remote\"`, or omit the field to use the default environment.",
+      "type": [
+        "string",
+        "null"
+      ]
+    },
     "ephemeral": {
       "type": [
         "boolean",