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/ContentView.swift

@@ -486,12 +486,12 @@ struct ContentView: View {
             ZStack(alignment: .top) {
                 rootTabView
                 if let banner = activeBanner {
-                    // Floating just below the nav bar: overlays content (never
-                    // pushes it) and stays clear of the iOS 26 nav/toolbar
-                    // Liquid Glass chrome so a tap on the banner can't also
-                    // trigger the control behind it.
+                    // Floating near the top of the screen, over the nav area —
+                    // overlays content (never pushes it) and sits above the
+                    // main content so it doesn't cover or block the list/pill
+                    // beneath it.
                     floatingBanner(banner)
-                        .padding(.top, geo.safeAreaInsets.top + 52)
+                        .padding(.top, geo.safeAreaInsets.top + 10)
                         .transition(.asymmetric(
                             insertion: .move(edge: .top).combined(with: .opacity),
                             // Slide up + fade on dismiss/timeout (one style for all).