phsl / new-api

The previous patch lower-cased `group` and `model` when building the
temporary `abilitySet` used to prevent duplicate inserts.
This merged models that differ only by letter case, e.g.
`GPT-3.5-turbo` vs `gpt-3.5-turbo`, causing them to disappear from the
user’s available-models list and pricing page.

Change:
• ability.go – removed all `strings.ToLower` calls when composing the
  deduplication key (`group|model`), so duplicates are checked in a
  case-sensitive manner while preserving the original data.

Result:
• `GPT-3.5-turbo` and `gpt-3.5-turbo` are now treated as distinct
  models throughout the system.