fix: allow unknown fields on Notice in schema (#10041)

the `notice` field didn't allow unknown fields in the schema, leading to
issues where they shouldn't be.

Now we allow unknown fields.

<img width="2260" height="720" alt="image"
src="https://github.com/user-attachments/assets/1de43b60-0d50-4a96-9c9c-34419270d722"
/>

codex-rs/core/config.schema.json

@@ -441,7 +441,6 @@
       "type": "object"
     },
     "Notice": {
-      "additionalProperties": false,
       "description": "Settings for notices we display to users via the tui and app-server clients (primarily the Codex IDE extension). NOTE: these are different from notifications - notices are warnings, NUX screens, acknowledgements, etc.",
       "properties": {
         "hide_full_access_warning": {