feat(FN-1862): add completion state tracking for onboarding

- Add markOnboardingCompleted() to set completedAt timestamp when user finishes onboarding
- Add isOnboardingCompleted() to check if onboarding was completed (vs dismissed)
- Update ModelOnboardingModal to call markOnboardingCompleted on successful completion
- Skip onboarding auto-open when already completed locally
- Add completion state tracking tests in ModelOnboardingModal.test.tsx
- Add model-onboarding-state unit tests
- Update useAuthOnboarding to check local completion state before auto-opening
- Document localStorage completion state tracking pattern in .fusion/memory.md

packages/dashboard/app/components/CustomModelDropdown.tsx

@@ -95,6 +95,11 @@ export function CustomModelDropdown({
   }, [favoriteModels, filteredModels]);
 
   // Sort providers: favorites first (in order), then alphabetically
+  // Exclude providers that are already favorited as models (they appear at top as pinned rows)
+  const favoritedProviderSet = new Set(favoriteModels.map((fullId) => {
+    const idx = fullId.indexOf("/");
+    return idx !== -1 ? fullId.slice(0, idx) : fullId;
+  }));
   const sortedProviderEntries = useMemo(() => {
     const entries = Object.entries(modelsByProvider);
     const favoritesSet = new Set(favoriteProviders);