Real iPhone wallpaper + populated Favourites captures

- PreviewWallpaper image set: the actual iPhone wallpaper extracted from the
  iOS 26.3 sim runtime (ActionButtonSelector Display.ca, 1320x2870 native
  res, JPEG ~180 KB) — replaces the gradient backdrop in the widget mock
- -seedFavourite <substring> launch hook: pins the first matching station
  for Unleaded via the normal keychain+app-group save path, so the
  Favourites tab can be captured populated (Ring Road Service Station,
  129.9, 59.1 mi, TOP badge)
- Re-captured 2-favourites (light), 6-favourites-dark, 9-widgets-dark,
  10-widgets-light with real data
- 95/95 tests green; Release IPA rebuilt + re-served

FuelBoard/Assets.xcassets/PreviewWallpaper.imageset/Contents.json

@@ -0,0 +1,13 @@
+{
+  "images" : [
+    {
+      "filename" : "PreviewWallpaper.jpg",
+      "idiom" : "universal",
+      "scale" : "1x"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}