[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/Services/PublicLocationModels.swift

@@ -28,6 +28,12 @@ struct PublicStoreListItem: Decodable, Sendable, Identifiable {
     let deliveryTime: String?
     let deliveryFee: Double?
     let minOrder: Double?
+    /// Kilometres from the picked city's centroid to the store - always
+    /// approximate, since the origin is the city rather than the visitor.
+    /// The server sends `0` for "unavailable" and never null; optional here
+    /// only so the app keeps decoding responses from before the field
+    /// shipped. See docs/plans/public-store-distance-consumer.md.
+    let distance: Double?
 }
 
 struct PublicStoreDetail: Decodable, Sendable {
@@ -56,6 +62,9 @@ struct PublicStoreDetail: Decodable, Sendable {
     let deliveryPrice: Double?
     let minOrder: Double?
     let acceptPix: Bool?
+    /// Same contract as `PublicStoreListItem.distance`, but only populated
+    /// when the detail request carries `state`/`city`.
+    let distance: Double?
 }
 
 // Maps the public (anonymous) store-detail projection onto the same models