feat(tv): add corner spotlight backdrop option (#1628)

New TV-only Appearance toggle that pins the spotlight artwork to the
top-right corner (68% width, 72% height) with the left and bottom edges
feathered into the scaffold background, so the logo, metadata, and
shelves sit on a calm surface instead of the image. Default is off —
the full-bleed spotlight stays exactly as it is.

The artwork keeps its full-screen request size: the corner box only
crops the layout, so transcode URLs and image caches are unchanged and
toggling the setting stays instant.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

lib/i18n/de.i18n.json

@@ -108,6 +108,8 @@
     "libraryDensity": "Mediathekdichte",
     "compact": "Kompakt",
     "comfortable": "Großzügig",
+    "tvCornerSpotlightBackdrop": "Backdrop in der Ecke",
+    "tvCornerSpotlightBackdropDescription": "Zeigt das Spotlight-Artwork oben rechts statt bildschirmfüllend",
     "viewMode": "Ansichtsmodus",
     "gridView": "Raster",
     "listView": "Liste",