Keep playlist affordances where an empty list took them

Three things live testing found, all of them where a playlist list or a
playlist is empty.

The picker said "This playlist has no videos" when there were no
playlists to pick — copy about a playlist's contents standing in for
copy about the list of them. Each section now says it has none, scoped
to where it is: the device, or that account. An account whose fetch came
back empty said nothing at all and left a bare gap.

The browse view's Playlists tab fetched into its own state, so a
playlist created through the picker — which goes through the shared
cache — never appeared, and nothing refetched on coming back to the tab.
It reads the cache now, and selecting the tab always refetches with the
rows already there kept on screen. The cache is keyed by account, which
is the discard on an account change the private copy needed a generation
for.

Removing the last video from a playlist took away the whole action row,
so an owned server-side playlist could no longer be renamed or deleted
from the app at all. The menu stays; only what needs videos to act on —
play, download, save to library — goes.

Yattee/Views/Playlist/UnifiedPlaylistDetailView.swift

@@ -466,9 +466,13 @@ struct UnifiedPlaylistDetailView: View {
                     .foregroundStyle(.secondary)
             }
 
-            // Action buttons row (iOS/macOS only)
+            // Action buttons row (iOS/macOS only).
+            //
+            // An owned playlist keeps its row after the last video is removed:
+            // renaming and deleting it are the only things left to do with it,
+            // and the row is where both live.
             #if !os(tvOS)
-            if !videos.isEmpty || localPlaylist != nil {
+            if !videos.isEmpty || localPlaylist != nil || canEditRemotePlaylist {
                 playlistActionButtons
             }
             #endif
@@ -482,51 +486,54 @@ struct UnifiedPlaylistDetailView: View {
     @ViewBuilder
     private var playlistActionButtons: some View {
         HStack(spacing: 12) {
-            // Play button (only when queue is enabled)
-            if isQueueEnabled {
-                Button {
-                    playAll()
-                } label: {
-                    Label(String(localized: "playlist.play"), systemImage: "play.fill")
-                        .fontWeight(.semibold)
+            // Playing and downloading need videos to act on; the menu does not.
+            if !videos.isEmpty {
+                // Play button (only when queue is enabled)
+                if isQueueEnabled {
+                    Button {
+                        playAll()
+                    } label: {
+                        Label(String(localized: "playlist.play"), systemImage: "play.fill")
+                            .fontWeight(.semibold)
+                    }
+                    .buttonStyle(.borderedProminent)
                 }
-                .buttonStyle(.borderedProminent)
-            }
 
-            // Download button with three states
-            if downloadCoordinator.isDownloading {
-                Button {
-                    // No action while downloading
-                } label: {
-                    HStack(spacing: 6) {
-                        ProgressView()
-                            .controlSize(.small)
-                        if let progress = downloadCoordinator.progress {
-                            Text("\(progress.current)/\(progress.total)")
-                                .monospacedDigit()
+                // Download button with three states
+                if downloadCoordinator.isDownloading {
+                    Button {
+                        // No action while downloading
+                    } label: {
+                        HStack(spacing: 6) {
+                            ProgressView()
+                                .controlSize(.small)
+                            if let progress = downloadCoordinator.progress {
+                                Text("\(progress.current)/\(progress.total)")
+                                    .monospacedDigit()
+                            }
                         }
                     }
+                    .fontWeight(.semibold)
+                    .buttonStyle(.bordered)
+                    .disabled(true)
+                } else if cachedAllVideosDownloaded {
+                    Button {
+                        // No action - already downloaded
+                    } label: {
+                        Label(String(localized: "playlist.downloaded"), systemImage: "checkmark.circle.fill")
+                    }
+                    .fontWeight(.semibold)
+                    .buttonStyle(.bordered)
+                    .disabled(true)
+                } else {
+                    Button {
+                        downloadCoordinator.startDownload(videos: videos)
+                    } label: {
+                        Label(String(localized: "playlist.downloadAll"), systemImage: "arrow.down.circle")
+                    }
+                    .fontWeight(.semibold)
+                    .buttonStyle(.bordered)
                 }
-                .fontWeight(.semibold)
-                .buttonStyle(.bordered)
-                .disabled(true)
-            } else if cachedAllVideosDownloaded {
-                Button {
-                    // No action - already downloaded
-                } label: {
-                    Label(String(localized: "playlist.downloaded"), systemImage: "checkmark.circle.fill")
-                }
-                .fontWeight(.semibold)
-                .buttonStyle(.bordered)
-                .disabled(true)
-            } else {
-                Button {
-                    downloadCoordinator.startDownload(videos: videos)
-                } label: {
-                    Label(String(localized: "playlist.downloadAll"), systemImage: "arrow.down.circle")
-                }
-                .fontWeight(.semibold)
-                .buttonStyle(.bordered)
             }
 
             Spacer()
@@ -535,16 +542,19 @@ struct UnifiedPlaylistDetailView: View {
             Menu {
                 // Remote-only: Save to Library, Share
                 if case .remote = source, let remotePlaylist, !remotePlaylist.isLocal {
-                    Button {
-                        Task { await importToLocal() }
-                    } label: {
-                        if isImporting, let progress = importProgress {
-                            Label(String(localized: "playlist.savingToLibrary \(progress.current) \(progress.total)"), systemImage: "plus.rectangle.on.folder")
-                        } else {
-                            Label(String(localized: "playlist.saveToLibrary"), systemImage: "plus.rectangle.on.folder")
+                    // Nothing to copy out of an empty playlist.
+                    if !videos.isEmpty {
+                        Button {
+                            Task { await importToLocal() }
+                        } label: {
+                            if isImporting, let progress = importProgress {
+                                Label(String(localized: "playlist.savingToLibrary \(progress.current) \(progress.total)"), systemImage: "plus.rectangle.on.folder")
+                            } else {
+                                Label(String(localized: "playlist.saveToLibrary"), systemImage: "plus.rectangle.on.folder")
+                            }
                         }
+                        .disabled(isImporting)
                     }
-                    .disabled(isImporting)
 
                     ShareLink(item: playlistShareURL()) {
                         Label(String(localized: "common.share"), systemImage: "square.and.arrow.up")
@@ -627,7 +637,9 @@ struct UnifiedPlaylistDetailView: View {
                     .foregroundStyle(.secondary)
             }
 
-            if !isDescriptionScrollLocked, !videos.isEmpty || localPlaylist != nil {
+            // An owned playlist keeps its buttons after the last video is
+            // removed: editing and deleting are all that is left to do with it.
+            if !isDescriptionScrollLocked, !videos.isEmpty || localPlaylist != nil || canEditRemotePlaylist {
                 tvOSPlaylistActionButtons
             }
 
@@ -685,8 +697,8 @@ struct UnifiedPlaylistDetailView: View {
     @ViewBuilder
     private var tvOSPlaylistActionButtons: some View {
         VStack(spacing: 12) {
-            // Play (only when queue is enabled)
-            if isQueueEnabled {
+            // Play (only when queue is enabled, and only with something to play)
+            if isQueueEnabled, !videos.isEmpty {
                 Button {
                     playAll()
                 } label: {
@@ -698,7 +710,7 @@ struct UnifiedPlaylistDetailView: View {
             }
 
             // Remote-only: Save to Library
-            if case .remote = source, let remotePlaylist, !remotePlaylist.isLocal {
+            if case .remote = source, let remotePlaylist, !remotePlaylist.isLocal, !videos.isEmpty {
                 Button {
                     Task { await importToLocal() }
                 } label: {