* 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)
* fix(web,api): support bare-array responses in fetchOpenAICompatibleModels
* fix(web,api): tighten maskAPIKeyValue to match maskAPIKey policy
For 9-12 character keys, maskAPIKeyValue exposed first 4 + last 4
chars (only 1 char masked for a 9-char key). Now uses the same
policy as maskAPIKey: first 3 + last 2 for 9-12 chars, first 3 +
last 4 for longer keys. Adds tests covering all key length boundaries.
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