Widget preview screen + shared widget rendering; dark-mode screenshots with real data

- Move widget entry view into Shared/FuelPriceWidgetViews.swift (FuelPriceWidgetContent,
  FuelPriceWidgetEntryData) so the app can render the REAL widget faces; widget
  extension now wraps it (FuelPriceEntry.data) — one source of truth for the face
- WidgetMockScreen (-widgets launch arg): app icon + small + medium widget previews
  for App Store captures; AppIconPreview image set (1024 drip master)
- AppStoreScreenshots: 5-8 dark-mode tab captures with real Halifax data, 9 widgets
- 95/95 tests green; Release IPA rebuilt + re-served

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

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