Add tvOS Top Shelf extension

Surfaces Continue Watching, Recent Feed, and Recent Bookmarks in the
Apple TV Home top shelf when Yattee is focused. Tapping a tile opens
the video via the existing yattee://video/{id} deep link.

- New YatteeTopShelf app extension target (tvOS only). LD_ENTRY_POINT is
  overridden to _NSExtensionMain; the tv-app-extension product type
  defaults to _TVExtensionMain which is for the pre-tvOS-13 legacy API
  and crashes modern TVTopShelfContentProvider subclasses at launch.
- Main app writes per-section JSON snapshots (capped at 10 items each)
  to a shared App Group UserDefaults suite after bookmark, watch-history,
  and feed-cache changes, plus an initial write on launch.
- Enabled-sections list is mirrored to the same App Group so the
  extension can respect the user's selection without touching SwiftData.
- Settings → Top Shelf (tvOS only) lets the user toggle sections.
- Deep link playback shows a loading toast while video details are
  fetched, and an error toast if no source is configured.

YatteeTopShelf/TopShelfContentProvider.swift

@@ -0,0 +1,38 @@
+import TVServices
+
+class TopShelfContentProvider: TVTopShelfContentProvider {
+    override func loadTopShelfContent(completionHandler: @escaping (any TVTopShelfContent) -> Void) {
+        let defaults = AppGroup.defaults
+        let enabled = TopShelfSnapshot.enabledSections(from: defaults)
+
+        let collections: [TVTopShelfItemCollection<TVTopShelfSectionedItem>] = enabled.compactMap { section in
+            let items = TopShelfSnapshot.read(section: section, from: defaults)
+            guard !items.isEmpty else { return nil }
+            let sectioned = items.map { makeItem(from: $0, in: section) }
+            let collection = TVTopShelfItemCollection(items: sectioned)
+            collection.title = section.localizedTitle
+            return collection
+        }
+
+        completionHandler(TVTopShelfSectionedContent(sections: collections))
+    }
+
+    private func makeItem(from item: TopShelfItem, in section: TopShelfSection) -> TVTopShelfSectionedItem {
+        let sectioned = TVTopShelfSectionedItem(identifier: "\(section.rawValue).\(item.videoID)")
+        sectioned.title = item.title
+        sectioned.imageShape = .hdtv
+        if let url = item.thumbnailURL.flatMap(URL.init(string:)) {
+            sectioned.setImageURL(url, for: .screenScale1x)
+            sectioned.setImageURL(url, for: .screenScale2x)
+        }
+        if let deepLink = URL(string: item.deepLinkURL) {
+            sectioned.displayAction = TVTopShelfAction(url: deepLink)
+            sectioned.playAction = TVTopShelfAction(url: deepLink)
+        }
+        if section == .continueWatching,
+           let progress = item.progressSeconds, item.duration > 0 {
+            sectioned.playbackProgress = max(0, min(1, progress / item.duration))
+        }
+        return sectioned
+    }
+}