banner: top-floating; fix offline-trigger cache; onboarding prompt timing

- Banner floats at the very top (over the nav/title area), never pushing the
  content below and staying clear of the list/pill.
- Offline banner now fires on refresh in airplane mode / no data: the mirror
  live chain bypassed the HTTP cache (+10s timeout) so an offline fetch really
  fails instead of silently re-serving a cached pointer+dump as a 'success'
  (which kept dataStatus .live and hid the banner).
- Onboarding permissions fire at the Continue/Allow tap BEFORE advancing, so
  the system prompt appears after the page is read and never covers the next
  page's animation (grant auto-advances).

FuelBoard/OnboardingView.swift

@@ -245,19 +245,27 @@ struct OnboardingView: View {
             ) {
                 if prompter.locationDenied {
                     openSettings()
+                } else if prompter.locationGranted {
+                    page = 2  // already decided — just move on
                 } else {
-                    // The prompt fires on LEAVING this page (onChange(of:
-                    // page), forward advance only) — the description is on
-                    // screen until the user moves on.
-                    page = 2
+                    // Fire the system prompt NOW, while this page is still on
+                    // screen (after it's been read) and BEFORE advancing — so
+                    // the prompt never covers the next page's animation. Auto-
+                    // advance on grant moves us on once the user responds;
+                    // denying leaves the page's "Open Settings" path.
+                    prompter.requestLocation()
                 }
             }
         case 2:
             primaryButton(
                 prompter.notificationsDenied ? "Continue without alerts" : (prompter.notificationsGranted ? "Continue" : "Allow Notifications")
             ) {
-                // Prompt fires on leaving this page (same rule as Location).
-                page = 3
+                if prompter.notificationsDenied || prompter.notificationsGranted {
+                    page = 3  // decided either way — move on
+                } else {
+                    // Same rule as Location: prompt now, before advancing.
+                    prompter.requestNotifications()
+                }
             }
         case 3:
             // No permission on this page — prices need none. Straight on.