Seller Detail Provider

FutureProvider.family keyed by handle that fetches /store/seller/{handle} (full profile + products + reviews) for the SellerDetailScreen.

1. ref.watch(sellerDetailProvider(handle)) on the detail screen.
2. Provider hits /store/seller/{handle} and returns the typed Seller-detail map.
3. Family entry stays cached unless invalidated — back-and-forth navigation is instant.

• Handle conflict (two sellers with the same handle) is a backend bug — client falls back to the first match.
• 404 returns a typed error inside AsyncValue.error which the screen renders as 'Seller not found'.

• lib/src/features/shared/search/providers/seller_detail_provider.dart

ref.invalidate(sellerDetailProvider(handle)) after a follow/unfollow to force a re-fetch with the updated followers count.