Widgets configured per-instance via App Intent

FuelPriceWidget now uses AppIntentConfiguration with a per-widget
FuelBoardWidgetConfigurationIntent (fuel + sort). Each widget placed on
the home screen carries its OWN fuel type (Unleaded/Premium/Diesel) and
ordering (Cheapest/Closest), edited by long-press -> Edit Widget —
independent of the app's selection, so multiple widgets can show
different data side by side. Widget no longer reads the app's selected
fuel. 35 tests pass.

FuelBoardWidgets/WidgetConfigIntent.swift

@@ -0,0 +1,45 @@
+import AppIntents
+import Foundation
+
+// Per-widget configuration intent (iOS 17+). Every widget instance carries
+// its OWN fuel + sort choices, edited directly on the home screen (long-press
+// → Edit Widget), independent of what the app has selected. This is what
+// allows several FuelBoard widgets to show different fuels/orderings side by
+// side.
+
+enum WidgetFuel: String, AppEnum, CaseIterable, Codable {
+    case e10
+    case e5
+    case diesel
+
+    static var typeDisplayRepresentation: TypeDisplayRepresentation = "Fuel"
+
+    static var caseDisplayRepresentations: [WidgetFuel: DisplayRepresentation] = [
+        .e10: "Unleaded",
+        .e5: "Premium",
+        .diesel: "Diesel",
+    ]
+}
+
+enum WidgetSort: String, AppEnum, CaseIterable, Codable {
+    case cheapest
+    case closest
+
+    static var typeDisplayRepresentation: TypeDisplayRepresentation = "Sort by"
+
+    static var caseDisplayRepresentations: [WidgetSort: DisplayRepresentation] = [
+        .cheapest: "Cheapest",
+        .closest: "Closest",
+    ]
+}
+
+struct FuelBoardWidgetConfigurationIntent: WidgetConfigurationIntent {
+    static var title: LocalizedStringResource = "Fuel & Sort"
+    static var description = IntentDescription("Which fuel and ordering this widget shows.")
+
+    @Parameter(title: "Fuel", default: .e10)
+    var fuel: WidgetFuel
+
+    @Parameter(title: "Sort by", default: .cheapest)
+    var sort: WidgetSort
+}