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)

FuelBoard/SettingsView.swift

@@ -60,6 +60,9 @@ struct SettingsView: View {
     /// Hidden developer flag — the Debug section only appears when on. Toggled
     /// by tapping the About → Version row five times (NOT a user-facing switch).
     @State private var debugMode: Bool = FuelStore.loadDebugMode()
+    /// Dev-only: re-inserts the LAN relay into the live chain (off by default —
+    /// consumers must never attempt local-network access).
+    @State private var relayFallbackEnabled: Bool = FuelStore.loadRelayFallbackEnabled()
     @State private var versionTapCount = 0
     @State private var lastVersionTap = Date.distantPast
     /// Widget diagnostics: the extension's last makeEntry beacon PER intent
@@ -129,6 +132,10 @@ struct SettingsView: View {
 
                 if debugMode {
                     Section {
+                        Toggle("LAN relay fallback (dev)", isOn: $relayFallbackEnabled)
+                            .onChange(of: relayFallbackEnabled) { _, enabled in
+                                FuelStore.saveRelayFallbackEnabled(enabled)
+                            }
                         Button {
                             sendTestAlert()
                         } label: {