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.

Yattee/Views/Settings/TopShelfSettingsView.swift

@@ -0,0 +1,52 @@
+//
+//  TopShelfSettingsView.swift
+//  Yattee
+//
+//  tvOS-only Top Shelf configuration.
+//
+
+#if os(tvOS)
+import SwiftUI
+
+struct TopShelfSettingsView: View {
+    @Environment(\.appEnvironment) private var appEnvironment
+
+    var body: some View {
+        Form {
+            if let settings = appEnvironment?.settingsManager {
+                Section {
+                    ForEach(TopShelfSection.allCases) { section in
+                        Toggle(section.localizedTitle, isOn: binding(for: section, settings: settings))
+                    }
+                } header: {
+                    Text(String(localized: "settings.topShelf.sections.header", defaultValue: "Sections"))
+                } footer: {
+                    Text(String(
+                        localized: "settings.topShelf.sections.footer",
+                        defaultValue: "Enabled sections appear in the Apple TV Home top shelf when Yattee is focused."
+                    ))
+                }
+            }
+        }
+    }
+
+    private func binding(for section: TopShelfSection, settings: SettingsManager) -> Binding<Bool> {
+        Binding(
+            get: { settings.topShelfSections.contains(section) },
+            set: { enabled in
+                var sections = settings.topShelfSections
+                if enabled {
+                    if !sections.contains(section) {
+                        let defaultIndex = TopShelfSection.defaultOrder.firstIndex(of: section) ?? sections.endIndex
+                        let insertAt = min(defaultIndex, sections.count)
+                        sections.insert(section, at: insertAt)
+                    }
+                } else {
+                    sections.removeAll { $0 == section }
+                }
+                settings.topShelfSections = sections
+            }
+        )
+    }
+}
+#endif