### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

In the Admin UI "Add Model" flow, selecting a provider lists models that are already retired. `getProviderModels()` (`ui/litellm-dashboard/src/components/provider_info_helpers.tsx`) returns every cost-map entry whose `litellm_provider` matches the selected provider and does not filter on `deprecation_date`.

`deprecation_date` is an existing field in the cost map; 58 entries already carry it (e.g. `azure/gpt-3.5-turbo-0125`, deprecation_date `2025-03-31`, still present). Because the dropdown ignores it, models past their deprecation date keep being offered. SambaNova is the most visible case: 12 of its 17 listed entries are retired.

**Expected:** the dropdown excludes entries whose `deprecation_date` is in the past (or shows them disabled). This applies to every provider, not just SambaNova.

### Steps to Reproduce

``` 1. Open the Admin UI (/ui) → Models → Add Model 2. Select a provider that has deprecation_date-tagged models: - SambaNova, or Azure OpenAI, etc. 3. Observe that the model dropdown lists retired models, e.g.: - SambaNova: …