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/Views/ContentItemView.swift

@@ -13,10 +13,21 @@ struct ContentItemView: View {
 
     init(item: ContentItem) {
         self.item = item
-        if item.contentType == .video, let video = item.video {
-            _watchRequest = video.watchFetchRequest
+        // Only create FetchRequest for video items, not for all items
+        if item.contentType == .video, let videoID = item.video?.videoID {
+            let predicate = NSPredicate(format: "videoID = %@", videoID as CVarArg)
+            _watchRequest = FetchRequest<Watch>(
+                sortDescriptors: [],
+                predicate: predicate,
+                animation: .default
+            )
         } else {
-            _watchRequest = Video.fixture.watchFetchRequest
+            // Empty fetch request for non-video items
+            _watchRequest = FetchRequest<Watch>(
+                sortDescriptors: [],
+                predicate: NSPredicate(value: false),
+                animation: .default
+            )
         }
     }