Make Subscriptions view focusable on tvOS

Move the channel-link button and View Options into a top safe-area inset
on tvOS so they are reachable with the remote, mirroring the Continue
Watching pattern. Wrap chrome and content in focus sections with a
default-focus namespace so initial focus lands on the first video. Hide
the duplicate in-content section header on tvOS, and add
scrollClipDisabled to VideoListContainer so focus scaling on rows is
not clipped at the scroll edges.

Yattee/Views/Components/VideoListContainer.swift

@@ -58,6 +58,7 @@ struct VideoListContainer<Header: View, Content: View, Footer: View>: View {
                 footer()
             }
         }
+        .scrollClipDisabled()
         #else
         // iOS/macOS: Background overlay pattern
         backgroundStyle.color