Optimize SwiftUI performance throughout the app

This commit addresses multiple SwiftUI performance bottlenecks identified
through code analysis, focusing on view rendering efficiency, list
performance, and memory usage optimization.

Key improvements:

- HomeView: Optimize async task management using structured concurrency
  with async let to handle multiple Defaults updates in a single task

- VideoCell: Remove GeometryReader from VideoCellThumbnail to eliminate
  layout thrashing; change @ObservedObject to computed property for shared
  ThumbnailsModel

- ThumbnailView: Cache URL extension computation in init() instead of
  recalculating on every body evaluation

- FavoriteItemView: Replace filter().prefix() with early-exit loop and
  capacity reservation for significant performance gain on large lists

- ContentItemView: Optimize FetchRequest creation with direct predicate
  construction only for video items, empty predicate for others

- VideoPlayerView: Fix playerSize didSet trigger by moving
  updateSidebarQueue() calls to explicit onChange/onAppear handlers

- FeedView: Replace .unique() with Set-based deduplication for O(n)
  performance and reduced allocations

- VerticalCells: Remove expensive sorting on every redraw; items should
  be pre-sorted from source

These optimizations follow SwiftUI best practices by minimizing expensive
computations in view bodies, caching computed values, using efficient data
structures, and avoiding unnecessary redraws and layout passes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Shared/Home/HomeView.swift

@@ -115,30 +115,40 @@ struct HomeView: View {
             #endif
         }
         .onAppear {
-            Task {
-                for await _ in Defaults.updates(.favorites) {
-                    favoritesChanged.toggle()
-                }
-                for await _ in Defaults.updates(.widgetsSettings) {
-                    favoritesChanged.toggle()
-                }
+            updateTask = Task {
+                async let favoritesUpdates: Void = {
+                    for await _ in Defaults.updates(.favorites) {
+                        favoritesChanged.toggle()
+                    }
+                }()
+                async let widgetsUpdates: Void = {
+                    for await _ in Defaults.updates(.widgetsSettings) {
+                        favoritesChanged.toggle()
+                    }
+                }()
+                _ = await (favoritesUpdates, widgetsUpdates)
             }
         }
         .onDisappear {
             updateTask?.cancel()
         }
 
-        .onChange(of: player.presentingPlayer) { _ in
-            if player.presentingPlayer {
+        .onChange(of: player.presentingPlayer) { presenting in
+            if presenting {
                 updateTask?.cancel()
             } else {
-                Task {
-                    for await _ in Defaults.updates(.favorites) {
-                        favoritesChanged.toggle()
-                    }
-                    for await _ in Defaults.updates(.widgetsSettings) {
-                        favoritesChanged.toggle()
-                    }
+                updateTask = Task {
+                    async let favoritesUpdates: Void = {
+                        for await _ in Defaults.updates(.favorites) {
+                            favoritesChanged.toggle()
+                        }
+                    }()
+                    async let widgetsUpdates: Void = {
+                        for await _ in Defaults.updates(.widgetsSettings) {
+                            favoritesChanged.toggle()
+                        }
+                    }()
+                    _ = await (favoritesUpdates, widgetsUpdates)
                 }
             }
         }