P0: live provider chain — GitHub mirror primary, relay fallback, bundled dump last resort + app telemetry beacon

- MirrorFuelProvider: fetches CURRENT prices from raw.githubusercontent
  (latest.json pointer → history/<day>.json full dump), app-group day-cache
  so the ~2.8 MB dump is re-downloaded only when the mirror pushes a new day
- LiveChainProvider: full path (app refresh) GitHub → relay; focused path
  (background alert checks) relay-first so alerts never pull the full dump
  over mobile data; records which leg served for About + telemetry
- FuelBeacon: fire-and-forget X-Client app ping to the relay's existing
  widget-diag route (zero relay changes) — attribution + cadence on-LAN,
  silent skip off-LAN is the reachability datum; /stats app-hit spike =
  GitHub path failing
- Bundled dump: FuelBoardDump dataset (real 2026-08-15 snapshot, 8,022
  stations) + BundledDumpProvider + scripts/refresh_bundled_dump.sh —
  no-network last resort replaces the demo sample set
- ContentView: About meta from the chain; catch falls back cached → bundled
  → sample
- 89 tests (6 new: chain order x4, cache decision, beacon URL); Release
  build green; beacon route verified against the live relay (204 + logged)

FuelBoard/ContentView.swift

@@ -454,9 +454,10 @@ struct ContentView: View {
             stations = fetched
             FuelStore.saveStations(fetched)
             FuelStore.saveLastRefresh()
-            // Persist relay envelope metadata (source, station count, GOV.UK
-            // dataset update time) for the Settings → About section.
-            if let meta = RelayFuelProvider.latestMeta {
+            // Persist envelope metadata (source, station count, GOV.UK
+            // dataset update time) for the Settings → About section — the
+            // live chain records whichever leg served the fetch.
+            if let meta = LiveChainProvider.latestMeta {
                 FuelStore.saveRelayMeta(meta)
             }
             // Keep the keychain favourites fresh with the new prices — the
@@ -467,8 +468,14 @@ struct ContentView: View {
             WidgetCenter.shared.reloadAllTimelines()
             statusMessage = "Loaded \(fetched.count) stations · \(Date().formatted(date: .omitted, time: .shortened))"
         } catch {
-            statusMessage = "Live fetch failed: \(error.localizedDescription). Showing cached/sample data."
-            stations = FuelStore.loadStations().isEmpty ? SampleFuelProvider.sampleStations : FuelStore.loadStations()
+            statusMessage = "Live fetch failed: \(error.localizedDescription). Showing cached data."
+            if FuelStore.loadStations().isEmpty {
+                // No cached prices — last resort is the bundled REAL dump
+                // (stale but genuine), then the demo sample set.
+                stations = BundledDumpProvider.stations ?? SampleFuelProvider.sampleStations
+            } else {
+                stations = FuelStore.loadStations()
+            }
         }
         // Keep monitor geofences in sync with the freshest data.
         monitor.update(stations: stations, favourites: refreshedFavourites,