Widget shots: use the shipping app icon (light + dark variants)

- AppIconPreview now byte-identical to the real AppIcon.png (the preview
  had been pointing at an older Design/ export); added AppIconPreviewDark
  from AppIcon-dark.png so the mock shows the correct icon per appearance
- Re-captured 9-widgets-dark + 10-widgets-light
- 95/95 tests green; Release IPA rebuilt + re-served

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

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