Hosted instances set HERMES_INFERENCE_MODEL as a provision-time seed in
the container env. _config_model_target() previously went through
_resolve_model() (env-first), so on hosted VPS the sync target stayed
pinned to the seed and dashboard model changes never reached an open
chat -- the exact scenario the sync exists to fix. The sync target now
reads config.yaml first and only falls back to the env vars when config
has no model. Startup resolution (_resolve_model) is unchanged.