The Camoufox REST API server expects `listItemId` in the `POST /tabs`
body, but `_ensure_tab` was sending `sessionKey`. This caused a 400
Bad Request on every `browser_navigate` call.
The parameter name mismatch is visible in the same file: line 283
already reads `tab.get("listItemId")` when adopting existing tabs,
confirming the server-side field name.
Fixes#37960
