fix(kobo): send Kobo covers at the device's screen size

A Kobo asks for each cover at its screen size but always got the
400x600 grid thumbnail, so sleep screens and full-screen covers were
blurry. Scale the full cover to fit the requested box instead, behind a
new Full-size covers setting that is on by default. Drop the stale
UserStorage entries from the authorization matrix gap baseline.

Fixes #924

server/test/e2e/authorization-matrix/route-inventory/uncovered-routes.json

@@ -33,7 +33,6 @@
   "GET /annotations/:annotationId/sync-detail",
   "GET /annotations/books",
   "GET /annotations/export",
-  "GET /api/UserStorage/Metadata",
   "GET /api/v3/content/:contentId/annotations",
   "GET /app-info",
   "GET /app-settings/cross-platform-path-sanitization",
@@ -91,7 +90,6 @@
   "GET /hardcover/sync/status",
   "GET /hardcover/sync/stream",
   "GET /health",
-  "GET /kobo/:deviceToken/api/UserStorage/Metadata",
   "GET /kobo/:deviceToken/api/v3/content/:contentId/annotations",
   "GET /kobo/history",
   "GET /koreader/file-naming-pattern",