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)

Shared/FuelPriceProvider.swift

@@ -19,9 +19,9 @@ protocol FuelPriceProviding {
 }
 
 enum FuelPriceProvider {
-    /// Default: the keyless relay (full-UK Fuel Finder data). Falls back to
-    /// the England-wide sample set when the relay is unreachable.
-    static let active: FuelPriceProviding = RelayFuelProvider()
+    /// Default: the live chain — GitHub mirror (primary, off-LAN) → LAN
+    /// relay (fallback) → bundled dump (last resort in the app target).
+    static let active: FuelPriceProviding = LiveChainProvider()
 
     /// Decodes a relay payload into stations, applying the defensive price
     /// band. Internal so the unit-test target can exercise the guard.
@@ -296,12 +296,15 @@ struct FuelFinderProvider: FuelPriceProviding {
 enum FuelProviderError: LocalizedError {
     case notImplemented
     case relayUnavailable
+    case mirrorUnavailable
     var errorDescription: String? {
         switch self {
         case .notImplemented:
             return "Live Fuel Finder API not wired yet — activate with GOV.UK One Login credentials."
         case .relayUnavailable:
             return "FuelBoard Relay unreachable — showing cached/sample data."
+        case .mirrorUnavailable:
+            return "GitHub price mirror unreachable."
         }
     }
 }