Settings: concise copy and tighter hierarchy

Rewrite the Settings screen in short British English and remove the
duplicated paragraphs, keeping every control, binding and preference key as
it was.

- Fuel Savings: one-line descriptions for Best Value, average fuel economy,
  fill-up amount (worded for the unit in use) and minimum saving; one concise
  general explanation replaces the long footer; the orange "New comparison
  basis" notice is removed.
- Units: "Station sign" becomes "Pence per litre"; the combined paragraph
  becomes two contextual descriptions.
- Distances: "Accurate distances" becomes "Driving distances" with a short
  description; the route-request and search-radii paragraph is removed.
- Tap action: "Open map"/"More info" become "Directions"/"Station details"
  with a short description.
- Data checking: Standard and Smart summaries cut to one line each, one shared
  background-update note, duplicated footer removed.
- Replay onboarding: shorter description. Support FuelBoard untouched.

Copy and layout only: no calculations, ranking, refresh schedules, stored
values or persistence changed. New and reworded literals live in
FuelBoard/en.lproj/Localizable.strings.

Shared/DataRefreshMode.swift

@@ -16,9 +16,9 @@ enum DataRefreshMode: String, CaseIterable, Identifiable {
     var summary: String {
         switch self {
         case .standard:
-            return "Saves battery. Refreshes price data up to twice daily."
+            return "Saves battery by checking for new prices up to twice a day."
         case .smart:
-            return "Checks for newer data more often in the background and refreshes full prices only when an update is available."
+            return "Checks for new prices more often, keeping your data fresher."
         }
     }
 }