Widget tap relay via fuelboard:// scheme; full station names; no check-again

- WidgetKit widgets can only open their containing app — the Link URL is
  delivered to FuelBoard via onOpenURL, never opened directly in Maps. The
  widget now links to a registered fuelboard://directions?lat=&lng= URL,
  and FuelBoardApp forwards it to native maps://?daddr= directions.
  (http://maps.apple.com and raw maps:// both silently dropped in-app.)
- Widget rows (small + medium) now show the full station name (station.name)
  instead of just the brand.
- Onboarding network page: removed the 'Check again' secondary screen after
  the Local Network prompt — Open Settings remains the only retry path.
  35 tests pass.

FuelBoard/OnboardingView.swift

@@ -297,11 +297,6 @@ struct OnboardingView: View {
                     }
                 }
                 .disabled(prompter.dataLoading)
-                if prompter.dataDenied {
-                    Button("Check again") { prompter.requestDataAccess() }
-                        .font(.subheadline)
-                        .foregroundStyle(.secondary)
-                }
             }
         default:
             primaryButton("Start Using FuelBoard") { finish() }