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/Player/VideoPlayerView.swift

@@ -28,7 +28,7 @@ struct VideoPlayerView: View {
         #endif
     }
 
-    @State private var playerSize: CGSize = .zero { didSet { updateSidebarQueue() } }
+    @State private var playerSize: CGSize = .zero
     @State private var hoveringPlayer = false
     @State private var sidebarQueue = defaultSidebarQueueValue
 
@@ -104,14 +104,16 @@ struct VideoPlayerView: View {
                 content
                     .onAppear {
                         playerSize = geometry.size
+                        updateSidebarQueue()
                     }
             }
             .ignoresSafeArea(.all, edges: .bottom)
             #if os(iOS)
                 .frame(height: playerHeight.isNil ? nil : Double(playerHeight!))
             #endif
-                .onChange(of: geometry.size) { _ in
-                    self.playerSize = geometry.size
+                .onChange(of: geometry.size) { newSize in
+                    self.playerSize = newSize
+                    updateSidebarQueue()
                 }
             #if os(iOS)
                 .onChange(of: player.presentingPlayer) { newValue in