Add Continue Watching toggle to tab bar settings

Exposes ContinueWatchingView as an opt-in compact tab bar item,
hidden by default. Uses a short "Continue" label since the full
"Continue Watching" string does not fit as a tab bar title.

Yattee/Models/Navigation/SidebarMainItem.swift

@@ -181,6 +181,7 @@ enum SidebarMainItem: String, CaseIterable, Codable, Identifiable, Sendable {
         case .downloads: self = .downloads
         case .sources: self = .sources
         case .settings: self = .settings
+        case .continueWatching: self = .continueWatching
         }
     }
 }