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/Videos/ThumbnailView.swift

@@ -5,16 +5,14 @@ import SwiftUI
 struct ThumbnailView: View {
     var url: URL?
     private let thumbnails = ThumbnailsModel.shared
+    private let thumbnailExtension: String?
 
-    var body: some View {
-        if url != nil {
-            viewForThumbnailExtension
-        } else {
-            placeholder
-        }
+    init(url: URL?) {
+        self.url = url
+        self.thumbnailExtension = Self.extractExtension(from: url)
     }
 
-    var thumbnailExtension: String? {
+    private static func extractExtension(from url: URL?) -> String? {
         guard let url,
               let urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: false) else { return nil }
 
@@ -24,6 +22,14 @@ struct ThumbnailView: View {
         return pathComponents.last
     }
 
+    var body: some View {
+        if url != nil {
+            viewForThumbnailExtension
+        } else {
+            placeholder
+        }
+    }
+
     @ViewBuilder var viewForThumbnailExtension: some View {
         if AccountsModel.shared.app != .piped, thumbnailExtension != nil {
             if thumbnailExtension == "webp" {