fix(core) default RejectConfig.request_permissions (#14165)

## Summary
Adds a default here so existing config deserializes

## Testing
- [x] Added a unit test

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

@@ -149,6 +149,7 @@
                   "type": "boolean"
                 },
                 "request_permissions": {
+                  "default": false,
                   "type": "boolean"
                 },
                 "rules": {
@@ -160,7 +161,6 @@
               },
               "required": [
                 "mcp_elicitations",
-                "request_permissions",
                 "rules",
                 "sandbox_approval"
               ],