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.

FuelBoard/BestValueIntroView.swift

@@ -83,7 +83,7 @@ struct BestValueIntroContent: View {
                 .pickerStyle(.segmented)
 
                 slider(
-                    title: String(localized: "Typical fill-up", comment: "Best Value fill-up slider label"),
+                    title: String(localized: "Fill-up amount", comment: "Best Value fill-up slider label"),
                     readOut: fillUpText,
                     value: amountBinding,
                     range: FuelSavingsCalculator.fillAmountSliderRange(for: settings.preferredAmount.unit),