v4.1.51

Hide near-expired thumbnails with override

Parse SharePoint thumbnail expiry and hide thumbnails that are about to expire when a storage-level override is enabled. Store thumbnail expiry in model.Thumbnail.ExpiresAt and propagate parsing into OneDrive drivers (onedrive, onedrive_app, onedrive_sharelink_api). Add utilities in internal/thumbnail to extract tempauth expiry and op/thumbnail to normalize thumbnails, clip directory cache TTL and decide visibility for List/Get/UpdateSite flows. Add Storage.ThumbnailExpirationOverride DB field and driver config item (default true), plus a bootstrap patch to enable the flag for existing storages. Include tests for parsing, driver conversions, and list/get behavior.