Consumer chain: GitHub-only — relay removed from app+widget, Local Network permission gone

The LAN relay is unreachable from any phone outside the developer's LAN, so
for App Store users a relay fallback was dead weight AND harmful: attempting
the private IP fires the iOS Local Network prompt on a stranger's phone and
adds a timeout before the bundled dump. GitHub raw is reachable anywhere the
relay would be, and more reliably.

- LiveChainProvider: GitHub mirror first EVERYWHERE (focused alert path no
  longer relay-first); LAN relay only joins behind the hidden dev flag
  fuelboard.relayFallback (Settings → Debug, keychain-first, off by default)
- MirrorFuelProvider: focused() projection replaces the relay's server-side
  radius endpoint (fuel filter + within-radius + nearest-first + limit 500)
  — the alert path re-checks radius/fuel itself, so behaviour is identical
- Widget: fetchFocused/fetchFuelOnly now GitHub-first via the chain (day-cache
  shared through the app group); relay + widget-diag GET gated on the same
  dev flag — off-LAN widgets no longer attempt local network at all
- FuelBeacon: fires only when the dev flag is on — consumers make zero
  local-network attempts; /stats app-hit spike = GitHub down + dev flag on
- Onboarding: Local Network machinery removed entirely (no probe, no prompt,
  no 12 s stall) — data page is now informational: prices download from the
  internet, no permissions needed. Replay on cellular can no longer hang.
- Info.plist: NSLocalNetworkUsageDescription copy → optional dev-only wording
- 95 tests (6 new: relay-skip-when-disabled x2, focused prefer-mirror, mirror
  focused projection x3, beacon dev-flag gate)

Shared/FuelStore.swift

@@ -301,6 +301,7 @@ struct FuelStore {
     static let alertsFollowSearchKey = "fuelboard.alertsFollowSearch"  // Bool — alerts mirror the Stations-tab distance
     static let liveActivityFollowSearchKey = "fuelboard.liveActivityFollowSearch" // Bool — Live Activity mirrors the Stations-tab distance
     static let debugModeKey = "fuelboard.debugMode"         // Bool — hidden dev flag
+    static let relayFallbackKey = "fuelboard.relayFallback" // Bool — dev-only relay fallback
     static let liveActivityKey = "fuelboard.liveActivity"    // Bool — Live Activity toggle
     static let liveActivityFuelKey = "fuelboard.liveActivityFuel"    // FuelType raw value
     static let liveActivityRadiusKey = "fuelboard.liveActivityRadiusMiles" // Int miles (5/10/15)
@@ -552,6 +553,22 @@ struct FuelStore {
         saveString(enabled ? "1" : "0", service: debugModeKey)
     }
 
+    // MARK: Relay fallback (dev-only)
+
+    /// Dev-only switch: re-inserts the LAN relay into the live chain as a
+    /// fallback for home testing. OFF by default — consumers must never make
+    /// a local-network attempt (the relay is unreachable off the developer's
+    /// LAN, and the attempt itself would fire the iOS Local Network prompt).
+    /// Toggled from Settings → Debug; keychain-first so it survives the
+    /// delete → reinstall test loop like every other small setting.
+    static func loadRelayFallbackEnabled() -> Bool {
+        loadString(service: relayFallbackKey) == "1"
+    }
+
+    static func saveRelayFallbackEnabled(_ enabled: Bool) {
+        saveString(enabled ? "1" : "0", service: relayFallbackKey)
+    }
+
     // MARK: Favourites
 
     /// A favourite pins a station FOR ONE fuel type. Starring a row while