Deduplicate provider model options in Settings UI

[shadowbipnode]

Summary

Some providers can return duplicated model IDs from their models endpoint.

Example observed with Mistral:

• mistral-large-2512
• mistral-large-latest
• voxtral-mini-latest
• voxtral-mini-2507

React currently warns about duplicate keys in Settings.jsx when rendering <option> elements.

Impact

Minor UI/dev-console warning only.

The provider works and AI calls complete successfully, but duplicated keys should be cleaned up to avoid unsupported React rendering behavior.

Proposed fix

In Settings.jsx, make model option keys unique, for example:

{models.map((model, index) => (
  <option key={`${model.id}-${index}`} value={model.id}>