feat: split Tap action into its own Settings section

Moves the Tap station picker out of Units into a dedicated Tap
action section, with the tap descriptor text as its footer. Units
footer reverts to distances/prices only.

FuelBoard/SettingsView.swift

@@ -118,6 +118,13 @@ struct SettingsView: View {
                         WidgetCenter.shared.reloadAllTimelines()
                         WatchSyncManager.shared.pushSnapshot()
                     }
+                } header: {
+                    Text("Units")
+                } footer: {
+                    Text("Distances and search radii across the app, widget and alerts are shown in this unit. Prices can be shown as on a station sign (129.9) or in pounds and pence (£1.29⁹/L).")
+                }
+
+                Section {
                     Picker("Tap station", selection: $stationTapAction) {
                         ForEach(StationTapAction.allCases) { action in
                             Text(action.displayName).tag(action)
@@ -128,9 +135,9 @@ struct SettingsView: View {
                         FuelStore.saveStationTapAction(newValue)
                     }
                 } header: {
-                    Text("Units")
+                    Text("Tap action")
                 } footer: {
-                    Text("Distances and search radii across the app, widget and alerts are shown in this unit. Prices can be shown as on a station sign (129.9) or in pounds and pence (£1.29⁹/L). Tapping a station either opens directions straight away or shows its details first.")
+                    Text("Tapping a station either opens directions straight away or shows its details first.")
                 }
 
                 Section {