Merge the toast UX refactor from PR #4304 (by @Shine1i):
- Toast duration 5s default with close button (X) for manual dismiss
- Inline progress bar component (ModelLoadInlineStatus) shown in the
header after toast is dismissed
- Model switch warning only for image compatibility (not generic)
- activeThreadId tracked in store via ActiveThreadSync
- Loading state cleanup via resetLoadingUi helper
- Toast uses Infinity duration during loading with onDismiss handler
Re-applied non-GGUF download progress additions on top:
- getDownloadProgress for all models (not just GGUF)
- hasShownProgress flag, loadingModelRef race condition checks
- First poll at 500ms, bytes-only fallback when expected size unknown
9cbeecc16a