Unify capsule, station label and price rating styling

One adaptive tone palette and one shape rule now drive every capsule on
Stations, Favourites, the detail sheet and the Key.

- CapsuleTone: the light/dark palette pairs in one place, resolved through a
  UIColor dynamic provider so a List row that re-renders without rebuilding
  its body still follows an appearance switch. Every pair clears 4.5:1
  foreground-on-background in both appearances (4.96-6.72:1).
- AdaptiveCapsule: capsule at one drawn line, rounded rect at two or more,
  radius 8 -> 10, measuring content before padding so insets cannot inflate
  the line count.
- Listing verdict capsules move from white-on-muted-solid to the tinted
  palette, so Saves, Break even, Costs and Closest station read the same in
  the rows and in the detail sheet.
- Best Value is purple, not green: green stays reserved for a financial
  saving, which is what the Saves capsule beside it means.
- Price dots standardise to 12pt in the app (widget keeps its own 6pt dot;
  PriceRatingDot now takes a diameter so the difference is deliberate).
- Station labels are sentence case with their recommended symbols (medal, tag,
  location.north.fill, trophy) and StationLabelKind replaces the Key's
  string-literal dispatch, so renaming a label can no longer drop a row.
- Key says "Costs", matching the capsule's own headline (was "Costs more").

FuelBoardTests/Tests/FuelBoardSharedTests/FuelSavingsTests.swift

@@ -271,17 +271,51 @@ final class KeySheetContentTests: XCTestCase {
         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.")
+            // "Costs" — the listing capsule's own headline, not "Costs more".
+            .init(label: "Costs", description: "Filling up here costs more than at your closest station, including travel.")
         ])
         XCTAssertFalse(KeySheetContent.savings.contains { $0.label == "Small saving" })
     }
 
+    /// Every Key label is sentence case: the capsules are read as phrases, and an
+    /// all-caps set reads as shouting beside the sentence-case copy around it.
+    func testEveryKeyLabelIsSentenceCase() {
+        let labels = (KeySheetContent.priceRatings
+                      + KeySheetContent.savings
+                      + KeySheetContent.stationLabels).map(\.label)
+        for label in labels {
+            XCTAssertNotEqual(label, label.uppercased(),
+                              "\(label) must be sentence case, not all caps")
+        }
+        XCTAssertEqual(KeySheetContent.stationLabels.map(\.label),
+                       ["Best value", "Cheapest", "Closest station", "Top"])
+    }
+
+    /// The Key dispatches its indicators on `StationLabelKind`, so every kind must
+    /// have exactly one entry in the legend — and each entry's label must be the
+    /// kind's own, or the row would describe one label and draw another.
+    func testEveryStationLabelKindHasOneMatchingLegendEntry() {
+        XCTAssertEqual(StationLabelKind.allCases.count, KeySheetContent.stationLabels.count)
+        for kind in StationLabelKind.allCases {
+            let matches = KeySheetContent.stationLabels.filter { $0.label == kind.label }
+            XCTAssertEqual(matches.count, 1, "\(kind) must own exactly one legend entry")
+        }
+    }
+
+    /// Recommended symbols, pinned so a rename cannot silently blank a badge.
+    func testStationLabelKindsUseTheirRecommendedSymbols() {
+        XCTAssertEqual(StationLabelKind.bestValue.symbol, "medal")
+        XCTAssertEqual(StationLabelKind.cheapest.symbol, "tag")
+        XCTAssertEqual(StationLabelKind.closestStation.symbol, "location.north.fill")
+        XCTAssertEqual(StationLabelKind.top.symbol, "trophy")
+    }
+
     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.")
+            .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 station", description: "The nearest station by journey distance."),
+            .init(label: "Top", description: "The cheapest station in your Favourites for the selected fuel.")
         ])
     }