The five HTTP call sites in browser_camofox.py (_ensure_tab, _post,
_get, _get_raw, _delete) did not include Authorization headers, causing
403 Forbidden when the Camofox server has API key auth enabled.
Added _auth_headers() helper and wired it into all five call sites.
The health check endpoint (/health) is left without auth since it is
a connectivity probe, not a browser operation.
Regression test covers: header present when key set, absent when unset,
blank key produces empty headers.
Fixes#20476
