live activity: tint pump glyph by monitored fuel

Move FuelType.tintColor (green=unleaded #30D158, yellow=premium #FFD60A,
cyan=diesel #64D2FF) into Shared/FuelStore.swift so the app, widget, and
Live Activity all read one definition (was app-only in StationsView, so the
widget couldn't see it). Tint the Live Activity rich card pump icon and the
Dynamic Island compactLeading pump by context.state.fuel.tintColor.

FuelBoardWidgets/FuelBoardLiveActivityView.swift

@@ -41,7 +41,7 @@ struct FuelBoardLiveActivity: Widget {
                 }
             } compactLeading: {
                 Image(systemName: "fuelpump.fill")
-                    .foregroundStyle(.green)
+                    .foregroundStyle(context.state.fuel.tintColor)
             } compactTrailing: {
                 FuelBoardLiveActivityPriceView(context: context)
             } minimal: {
@@ -95,7 +95,7 @@ private struct FuelBoardLiveActivityView: View {
             // LEFT — station brand glyph
             Image(systemName: "fuelpump.circle.fill")
                 .font(.system(size: 32))
-                .foregroundStyle(.green, .white)
+                .foregroundStyle(context.state.fuel.tintColor, .white)
                 .frame(width: 40, height: 40)
 
             // MIDDLE — fuel + station