- Fix _call_provider to support custom providers (OpenAI-compatible
fallback) instead of raising ValueError for unknown providers
- Add POST /admin/ppt/sync-models endpoint that fetches available
models from the configured provider's API
- Redesign PptSettingsAdmin UI: replace Dify model dropdown with
per-provider 'sync models' button + searchable model selector
- Remove dead Dify-specific code (fetchDifyModels, applyDifyModel)
- Update deepseek default model from deepseek-chat to deepseek-v4-pro
- API Key field now always shown (not conditional on non-dify)