[good first issue] Add provider filter to Models tab

[GoDiao]

Summary

Add a provider dropdown filter to the Models tab so users can quickly find models available from a specific provider.

Background

The Models tab currently supports text search and sorting, but it does not let users filter by provider. Freeway supports many providers, so provider-level filtering makes the catalog easier to browse.

Relevant files:

• src/web/templates/index.html
• src/web/static/app.js
• src/web/static/style.css

Requirements

• Add a provider dropdown to the Models tab toolbar.
• Include an All providers default option.
• Build provider options from state.providers.
• Make provider filtering work together with existing search and sort controls.
• Keep the UI consistent with existing console controls.

Acceptance Criteria

• Users can filter models by provider.
• Search + provider filter + sort can be combined.
• The default view still shows all models.
• No new dependencies are added.
• npm run build passes.

Notes for Contributors

Start with renderModels() and renderTestModelOptions() in src/web/static/app.js.