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/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)
+    }
+}