Improve action menu escape handling

Make the F11 action menu close through a shared close action so Escape and the explicit Close actions menu item follow the same path. Treat Escape-prefixed Up and Down events as close inputs while the action menu is active, which handles termbox InputAlt behavior after pressing Escape. Preserve and restore the user/channel tree selection across action menu open and close, and preserve selection across live tree rebuilds.

Tested with: GOCACHE=/tmp/barnard-go-cache go test ./...

barnard.go

@@ -43,6 +43,7 @@ type Barnard struct {
 	selectedUser    *gumble.User
 	adminTargetUser *gumble.User
 	adminTargetChan *gumble.Channel
+	adminReturnItem uiterm.TreeItem
 	statusText      string
 	statusNotice    bool
 
@@ -144,7 +145,7 @@ func (b *Barnard) TreeItemKeyPress(ui *uiterm.Ui, tree *uiterm.Tree, item uiterm
 				delete(b.MutedChannels, treeItem.Channel.ID)
 			}
 
-			b.UiTree.Rebuild()
+			b.RebuildUserChannelTreePreservingSelection()
 			b.Ui.Refresh()
 		}
 		if key == *b.Hotkeys.VolumeDown {
@@ -169,7 +170,7 @@ func (b *Barnard) TreeItemKeyPress(ui *uiterm.Ui, tree *uiterm.Tree, item uiterm
 					treeItem.User.AudioSource.SetGain(treeItem.User.Volume)
 				}
 			}
-			b.UiTree.Rebuild()
+			b.RebuildUserChannelTreePreservingSelection()
 			b.Ui.Refresh()
 		}
 		if key == *b.Hotkeys.VolumeDown {