Add model catalog browsing, provider registry with form validation,
model fetch/test dialogs, and enhanced model management UI.
- Add model catalog API and catalog-dialog component for browsing saved models
- Add provider-registry with auto-populated form fields per provider
- Add provider-combobox, fetch-models-dialog, test-model-dialog components
- Add model-validation for provider-aware model ID validation
- Add command and popover UI components
- Enhance edit-model-sheet with tool schema transform support
- Add anthropic to protocolMetaByName for correct default API base
- Apply NormalizeBaseURL to anthropic provider for consistent URL handling
- Add i18n keys for new model management features (en/zh)
