[public-store-distance] Consume the public distance contract, stop labelling it as unavailable

Guest browsing showed 'Distância indisponível' on every store card and a
'--' tile on store detail, because the public locator response carries no
distance and StoreSummary.init(publicItem:) hardcoded nil.

Backend contract (docs/plans/public-store-distance-consumer.md): distance
is a number, never null, 0 means unavailable. Implemented app-side ahead of
the backend - every change is forward-compatible, and the part that removes
the broken label works with no backend at all.

- PublicStoreListItem / PublicStoreDetail: + distance (optional, so today's
  responses without the field still decode).
- StoreSummary.init(publicItem:): normalize the 0 sentinel to nil, so one
  representation of 'unknown' reaches the label and the max-distance filter.
- fetchStoreDetail: send state/city from GuestLocationStore by default -
  the server needs them to resolve the city centroid.
- formatDistance: empty string for nil/0/negative. It previously returned
  'Distância indisponível' for nil, and - found by the new test - '0 m' for
  0 and '-1000 m' for a negative.
- StoreCard: drop the distance segment and its '·' separator together,
  otherwise the row ended in a dangling separator.
- StoreDetailView: drop the DISTÂNCIA tile and its divider instead of '--'.

Also fixes the same label in the authenticated flow when the user declined
location and has no address coordinates.

Tests: PublicStoreDistanceTests (decode with/without the field, passthrough,
0 normalization) + the empty case in HomeViewFilteringTests.

PediFoods/Components/StoreCard.swift

@@ -53,12 +53,17 @@ struct FeaturedStoreCard: View {
                     Text("(\(store.reviews))")
                         .font(.caption)
                         .foregroundStyle(AppColors.textMuted)
-                    Text("·")
-                        .font(.caption)
-                        .foregroundStyle(AppColors.textMuted)
-                    Text(store.distance)
-                        .font(.caption)
-                        .foregroundStyle(AppColors.textMuted)
+                    // Empty distance means "unavailable" - drop the separator
+                    // with it, otherwise the row ends in a dangling "·".
+                    // See docs/plans/public-store-distance-consumer.md.
+                    if store.distance.isEmpty == false {
+                        Text("·")
+                            .font(.caption)
+                            .foregroundStyle(AppColors.textMuted)
+                        Text(store.distance)
+                            .font(.caption)
+                            .foregroundStyle(AppColors.textMuted)
+                    }
                 }
             } else {
                 Text(store.statusLabel?.isEmpty == false ? (store.statusLabel ?? "Fechado") : "Fechado")