When multiple providers expose the same bare model ID (e.g. two custom
providers both listing gpt-5.4), the model picker cannot distinguish
them — both rows appear active and clicking the other provider's copy
is a no-op.
Fix:
- Add _deduplicate_model_ids() post-process in api/config.py that
detects duplicate bare model IDs across groups and prefixes
collisions with @provider_id: so each entry is globally unique
- Update norm() regex in static/ui.js to strip @provider: prefixes
for fuzzy matching, so existing sessions with bare model IDs still
restore correctly
- First occurrence stays bare for backward compatibility with sessions
that already store the bare model name
- Update test_model_resolver to be dedup-aware
Closes#1228
