[UI Bug] Model selection UI unusable with cloud providers that expose 300+ models (e.g. OpenRouter) — no search, no grouping, no pagination, no selection feedback #999

Describe the bug
When using cloud providers like OpenRouter that expose 300–400 models, the language model selection UI becomes unusable. There is no search/filter functionality, no pagination or virtual scrolling, and no indication of which models are currently selected. Scrolling through hundreds of entries to find a specific model is impractical.

To Reproduce
Steps to reproduce the behavior:

1. Go to Settings → Language Models
2. Add OpenRouter as a cloud provider
3. Observe that 300–400 models populate the selection list
4. Attempt to find a specific model (e.g. anthropic/claude-sonnet-2026-04-01)
5. Scroll through the entire unsorted/flat list
6. See no search bar, no grouping, no pagination
7. Select a model — the UI gives no clear visual feedback on which models are currently enabled

Expected behavior

• Search/filter input to quickly narrow down models by name or provider prefix
• Grouping by provider (e.g. Anthropic, OpenAI, Meta) or category
• Virtual scrolling or pagination for performance
• Show the slug or the friendly name of the model, and ellipsize the description.
• Perhaps a "selected models" summary section

Screenshots

Desktop (please complete the following information):

• OS: Linux
• Browser: Firefox / Chrome
• Version: latest - 1.7.3
  Smartphone
  N/A

Additional context
OpenRouter exposes models like openai/gpt-4o, anthropic/claude-sonnet-4-20250514, meta-llama/llama-4-scout, etc. A flat list of 350+ entries with no search makes selection nearly impossible. Grouping by provider prefix (the string before /) would be a significant improvement.