Add feature flag to disable hide shorts functionality

The hide shorts feature is no longer working due to API changes that prevent reliable detection of short videos. This commit introduces a feature flag system to disable the functionality while preserving the ability to easily restore it if the API issue is resolved.

Changes:
- Add FeatureFlags.swift with hideShortsEnabled flag (currently disabled)
- Hide all HideShortsButtons UI elements when flag is disabled
- Disable shorts filtering logic in ContentItemView, FavoriteItemView, and FeedModel
- Preserve hideShorts user preference for future restoration

Shared/Views/ContentItemView.swift

@@ -54,7 +54,7 @@ struct ContentItemView: View {
             return false
         }
 
-        guard hideShorts, item.contentType == .video, let video = item.video else {
+        guard FeatureFlags.hideShortsEnabled, hideShorts, item.contentType == .video, let video = item.video else {
             return true
         }
 

Shared/Views/HideShortsButtons.swift

@@ -5,22 +5,24 @@ struct HideShortsButtons: View {
     @Default(.hideShorts) private var hideShorts
 
     var body: some View {
-        Button {
-            hideShorts.toggle()
-        } label: {
-            Group {
-                if hideShorts {
-                    Label("Short videos: hidden", systemImage: "bolt.slash.fill")
-                        .help("Short videos: hidden")
-                } else {
-                    Label("Short videos: visible", systemImage: "bolt.fill")
-                        .help("Short videos: visible")
+        if FeatureFlags.hideShortsEnabled {
+            Button {
+                hideShorts.toggle()
+            } label: {
+                Group {
+                    if hideShorts {
+                        Label("Short videos: hidden", systemImage: "bolt.slash.fill")
+                            .help("Short videos: hidden")
+                    } else {
+                        Label("Short videos: visible", systemImage: "bolt.fill")
+                            .help("Short videos: visible")
+                    }
                 }
+                #if os(tvOS)
+                .font(.caption)
+                .imageScale(.small)
+                #endif
             }
-            #if os(tvOS)
-            .font(.caption)
-            .imageScale(.small)
-            #endif
         }
     }
 }