This fixes the 404 error on the settings page for the Perplexity provider by:
1. Removing the `model_list` validation check, as Perplexity does not support a standard `/models` endpoint compatible with the validator.
2. Hardcoding the list of supported Sonar models (`sonar`, `sonar-pro`, `sonar-reasoning-pro`, `sonar-deep-research`) in the provider capabilities.
3. Ensuring `sonar` is the first model in the list so it is used for connectivity health checks.
Changes applied to both `packages/stage-ui/src/libs/providers/providers/perplexity-ai/index.ts` and `packages/stage-ui/src/stores/providers.ts`.
Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: shinohara-rin <25588514+shinohara-rin@users.noreply.github.com>
