Retire the Best Value proximity alert option; move Key sheet copy into a tested model

- Alerts: drop the alert-type picker and the Best Value alert path, so
  proximity alerts always follow the cheapest station. A stored `bestValue`
  selection now falls back to cheapest when loaded.
- Key sheet: the price-rating, savings, station-label and favourite wording
  comes from `KeySheetContent` in Shared/FuelSavings.swift — a Foundation-only
  model with tests that pin the exact meaning of each indicator — and the
  sheet is built from that model rather than inline strings.
- BACKLOG: record the plan to restore Best Value proximity alerts behind one
  shared evaluator (user-location baseline, a single disclosed qualification
  rule, and real/Test alert parity).
- Bump CURRENT_PROJECT_VERSION to 29.

Shared/FuelSavings.swift

@@ -309,6 +309,42 @@ struct FuelSavingsRankedStation: Equatable {
     let pricePencePerLitre: Double
 }
 
+/// The user-facing copy shown by the Stations tab's Key sheet. Keeping the
+/// descriptions in one Foundation-only model lets tests pin the exact meaning of
+/// each visual indicator without coupling the wording to SwiftUI layout.
+enum KeySheetContent {
+    struct Item: Equatable {
+        let label: String
+        let description: String
+    }
+
+    static let priceRatings = [
+        Item(label: "Good price", description: "Within 1.5p/L of the cheapest."),
+        Item(label: "Okay", description: "More than 1.5p/L, up to 4p/L above the cheapest."),
+        Item(label: "Pricey", description: "More than 4p/L above the cheapest.")
+    ]
+
+    static let savings = [
+        Item(label: "Saves", description: "You’ll save money compared with your closest station, including travel costs."),
+        Item(label: "Break even", description: "The saving or extra cost is negligible."),
+        Item(label: "Costs more", description: "Filling up here costs more than at your closest station, including travel.")
+    ]
+
+    static let stationLabels = [
+        Item(label: "BEST VALUE", description: "Meets your minimum saving after travel costs."),
+        Item(label: "CHEAPEST", description: "The lowest fuel price per litre within your selected range."),
+        Item(label: "CLOSEST", description: "The nearest station by journey distance."),
+        Item(label: "TOP", description: "The cheapest station in your Favourites for the selected fuel.")
+    ]
+
+    static let favourite = Item(
+        label: "Favourites",
+        description: "Star a station to save it to your Favourites."
+    )
+
+    static let helpTitle = "How does Best Value work?"
+}
+
 /// Which recommendation badge a station listing row shows, if any.
 ///
 /// Presentation only — no new rules: the BEST VALUE qualification reuses the

Shared/FuelStore.swift

@@ -701,10 +701,12 @@ struct FuelStore {
     }
 
     static func loadAlertsMode() -> AlertMode {
-        if let raw = loadString(service: alertsModeKey), let mode = AlertMode(rawValue: raw) {
-            return mode
+        guard let raw = loadString(service: alertsModeKey),
+              let mode = AlertMode(rawValue: raw),
+              mode == .cheapest else {
+            return .cheapest
         }
-        return .cheapest
+        return mode
     }
 
     static func saveAlertsMode(_ mode: AlertMode) {