Live Activity: cheapest-in-radius Lock Screen/Dynamic Island pill

- Shared FuelBoardLiveActivityAttributes/ContentState (app + widget targets)
- FuelBoardLiveActivity Widget: ActivityConfiguration rendered by the widget
  extension - Lock Screen banner + Dynamic Island (leading/trailing/bottom,
  compact, minimal), tap anywhere -> maps:// directions to the best station
- LiveActivityManager (app side): request/update/end; mirrors the app list's
  TOP badge (selected fuel + chosen distance radius, price-then-distance
  ties); local start-date tracking for the 8h cap (this SDK's Activity has no
  startDate) - auto-restarts at 7h59m; silent no-op when disabled/denied
- Wiring: 250m/60s location hook (incl. background significant-change
  wake-ups), refresh completion, fuel/radius/unit changes, toggle flip
- Settings toggle + FuelStore persistence (keychain-backed, app-group)
- App-Info.plist: NSSupportsLiveActivities

FuelBoardWidgets/FuelBoardLiveActivityView.swift

@@ -0,0 +1,135 @@
+// FuelBoardLiveActivityView.swift — renders the FuelBoard Live Activity.
+//
+// Lives in the widget extension (the standard host for ActivityConfiguration).
+// Shows the cheapest station for the pinned fuel within the app's chosen
+// radius. Tapping anywhere opens Apple Maps directions to that station.
+
+import ActivityKit
+import SwiftUI
+import WidgetKit
+
+/// The Live Activity itself — registered in the widget bundle alongside the
+/// regular price widget. No CarPlay entitlement involved: this renders on the
+/// Lock Screen, Dynamic Island, and (iOS 26+ / CarPlay Ultra) the car display.
+struct FuelBoardLiveActivity: Widget {
+    var body: some WidgetConfiguration {
+        ActivityConfiguration(for: FuelBoardLiveActivityAttributes.self) { context in
+            // Lock Screen / banner presentation
+            FuelBoardLiveActivityView(context: context)
+        } dynamicIsland: { context in
+            DynamicIsland {
+                DynamicIslandExpandedRegion(.leading) {
+                    FuelBoardLiveActivityCompactView(context: context)
+                }
+                DynamicIslandExpandedRegion(.trailing) {
+                    FuelBoardLiveActivityPriceView(context: context)
+                }
+                DynamicIslandExpandedRegion(.bottom) {
+                    FuelBoardLiveActivityStationView(context: context)
+                }
+            } compactLeading: {
+                Image(systemName: "fuelpump.fill")
+                    .foregroundStyle(.green)
+            } compactTrailing: {
+                FuelBoardLiveActivityPriceView(context: context)
+            } minimal: {
+                Text(context.state.priceText)
+                    .font(.caption2.bold().monospacedDigit())
+            }
+        }
+    }
+}
+
+/// Lock Screen / banner body — the main presentation.
+private struct FuelBoardLiveActivityView: View {
+    let context: ActivityViewContext<FuelBoardLiveActivityAttributes>
+
+    var body: some View {
+        Link(destination: context.state.mapsURL) {
+            HStack(spacing: 12) {
+                // LEFT — station brand glyph
+                Image(systemName: "fuelpump.circle.fill")
+                    .font(.system(size: 32))
+                    .foregroundStyle(.green, .white)
+                    .frame(width: 40, height: 40)
+
+                // MIDDLE — fuel + station
+                VStack(alignment: .leading, spacing: 2) {
+                    Text("Cheapest \(context.attributes.fuel.displayName)")
+                        .font(.headline)
+                    Text("\(context.state.stationName) · \(context.state.distanceText)")
+                        .font(.subheadline)
+                        .foregroundStyle(.secondary)
+                        .lineLimit(1)
+                }
+                .frame(maxWidth: .infinity, alignment: .leading)
+
+                // RIGHT — price
+                VStack(alignment: .trailing, spacing: 2) {
+                    Text(context.state.priceText)
+                        .font(.title2.bold().monospacedDigit())
+                    Text("Tap for directions")
+                        .font(.caption2)
+                        .foregroundStyle(.secondary)
+                }
+            }
+            .padding()
+        }
+    }
+}
+
+/// Dynamic Island expanded regions + compact trailing — price only.
+private struct FuelBoardLiveActivityPriceView: View {
+    let context: ActivityViewContext<FuelBoardLiveActivityAttributes>
+
+    var body: some View {
+        Text(context.state.priceText)
+            .font(.headline.bold().monospacedDigit())
+    }
+}
+
+/// Dynamic Island expanded — fuel + station name.
+private struct FuelBoardLiveActivityCompactView: View {
+    let context: ActivityViewContext<FuelBoardLiveActivityAttributes>
+
+    var body: some View {
+        VStack(alignment: .leading, spacing: 2) {
+            Text("Cheapest \(context.attributes.fuel.displayName)")
+                .font(.caption2)
+                .foregroundStyle(.secondary)
+            Text(context.state.stationName)
+                .font(.caption.bold())
+                .lineLimit(1)
+        }
+    }
+}
+
+/// Dynamic Island expanded bottom — station + distance.
+private struct FuelBoardLiveActivityStationView: View {
+    let context: ActivityViewContext<FuelBoardLiveActivityAttributes>
+
+    var body: some View {
+        Text("\(context.state.stationName) · \(context.state.distanceText)")
+            .font(.caption)
+            .lineLimit(1)
+    }
+}
+
+// MARK: - ContentState display helpers
+
+extension FuelBoardLiveActivityAttributes.ContentState {
+    /// Display distance using the user's chosen unit (miles default).
+    var distanceText: String {
+        FuelStore.loadDistanceUnit().format(distanceKM)
+    }
+
+    /// £ price string from pence, e.g. 161.9 -> "£1.619".
+    var priceText: String {
+        String(format: "£%.3f", pricePence / 100)
+    }
+
+    /// Apple Maps directions URL to the pinned station.
+    var mapsURL: URL {
+        URL(string: "maps://?daddr=\(lat),\(lng)&t=d")!
+    }
+}