config: make a settings save reach the engine and the front

Configuring a remote capability in the UI did nothing until a restart,
which makes the feature unusable as shipped.

The admin API is served by the SYSTEM worker, so a save updates that
process's config object. The remote gateway, the engine blocks and the
front's burst-to-RunPod path all read a DIFFERENT process's copy. The
engine's /internal/reload-config — which the front pushes on a config
change — re-read models.json only, and the front's own refresh copied a
fixed field list that included neither `runpod` nor `remotes`.

Both now carry them: the engine re-reads config.json into its live config
on reload, and the front refreshes runpod/remotes along with the rest.

Found by trying to use the feature on the running instance rather than by
reading the code, which is the only way this class of bug shows up.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0182DhR1eFNPQyGmDrpHbedY