Add model metadata fields (top_provider, pricing, description, supported_parameters, architecture) and dashboard Get Models button

- Update providers.py to extract all fields from provider API responses
- Add max_input_tokens support for Claude provider context size
- Add top_provider, pricing, description, supported_parameters, architecture fields
- Update cache functions to save/load new metadata fields
- Update handlers.py to expose new fields in model list response
- Add Get Models button to dashboard