* feat(web,api): add fetch models and saved catalog support
Split from PR #2752 (part 2 of 3).
Backend:
- /api/models/catalog endpoint for browsing remote model catalogs
- /api/models/fetch endpoint for fetching available models from providers
- Credential reuse with provider/API base matching for security
- Default API base resolution for providers without explicit base
Frontend:
- FetchModelsDialog for importing models from remote providers
- CatalogDialog for browsing and importing from model catalogs
- Static import for FetchModelsDialog (replaces dynamic import from PR1)
- Dynamic import retained for TestModelDialog (PR3 territory)
* feat(web,api): add test connection with real connectivity verification
Split from PR #2752 (part 3 of 3).
Backend:
- /api/models/{index}/test endpoint for testing saved model configs
- /api/models/test-inline endpoint for testing unsaved form values
- Real network probe (GET /models) for connectivity verification
- Credential reuse with provider/API base matching for security
- Default API base resolution for providers without explicit base
Frontend:
- TestModelDialog for testing model connectivity
- Inline test support for add/edit model sheets
- Static import for TestModelDialog (replaces dynamic import from PR1)