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.

FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsTests.swift

@@ -257,3 +257,39 @@ final class StationRecommendationBadgeTests: XCTestCase {
         )
     }
 }
+
+final class KeySheetContentTests: XCTestCase {
+    func testPriceRatingsExplainTheImplementedRAGBoundaries() {
+        XCTAssertEqual(KeySheetContent.priceRatings, [
+            .init(label: "Good price", description: "Within 1.5p/L of the cheapest."),
+            .init(label: "Okay", description: "More than 1.5p/L, up to 4p/L above the cheapest."),
+            .init(label: "Pricey", description: "More than 4p/L above the cheapest.")
+        ])
+    }
+
+    func testSavingsExplainVerdictsWithoutImplyingMinimumSavingQualification() {
+        XCTAssertEqual(KeySheetContent.savings, [
+            .init(label: "Saves", description: "You’ll save money compared with your closest station, including travel costs."),
+            .init(label: "Break even", description: "The saving or extra cost is negligible."),
+            .init(label: "Costs more", description: "Filling up here costs more than at your closest station, including travel.")
+        ])
+        XCTAssertFalse(KeySheetContent.savings.contains { $0.label == "Small saving" })
+    }
+
+    func testStationLabelsDescribeTheCurrentQualificationAndRangeRules() {
+        XCTAssertEqual(KeySheetContent.stationLabels, [
+            .init(label: "BEST VALUE", description: "Meets your minimum saving after travel costs."),
+            .init(label: "CHEAPEST", description: "The lowest fuel price per litre within your selected range."),
+            .init(label: "CLOSEST", description: "The nearest station by journey distance."),
+            .init(label: "TOP", description: "The cheapest station in your Favourites for the selected fuel.")
+        ])
+    }
+
+    func testFavouriteAndHelpCopyRemainPinned() {
+        XCTAssertEqual(
+            KeySheetContent.favourite,
+            .init(label: "Favourites", description: "Star a station to save it to your Favourites.")
+        )
+        XCTAssertEqual(KeySheetContent.helpTitle, "How does Best Value work?")
+    }
+}

FuelBoardTests/Tests/FuelBoardSharedTests/FuelStoreTests.swift

@@ -31,3 +31,12 @@ final class FuelStoreBestValueThresholdTests: XCTestCase {
         }
     }
 }
+
+final class FuelStoreAlertModeTests: XCTestCase {
+    func testLegacyBestValueSelectionLoadsAsCheapest() {
+        FuelStore.saveAlertsMode(.bestValue)
+        defer { FuelStore.saveAlertsMode(.cheapest) }
+
+        XCTAssertEqual(FuelStore.loadAlertsMode(), .cheapest)
+    }
+}