Rework popups and fix blurry text and player list layout

Popups:
- All nine popups now extend a shared PopupWindow class with open(),
  close() and toggle(), instead of each copying its own close-on-click
  code. Popups that need cleanup override close().
- A click outside a popup closed it and also pressed whatever was
  underneath, e.g. Reset playlist. The closing click is now consumed.
- Popups used Godot's see-through default panel, so the song list and
  titles showed through. They now use an opaque popup theme, and a
  backdrop dims the window behind them.
- The main window root now fills the screen, so the backdrop covers it.

Text and images:
- Many labels and buttons forced nearest filtering, which made text and
  icons jagged when the window is not 1920x1080. They now use the
  default smooth filtering. Only the pixel-art "no character" picture
  keeps nearest filtering when the winner window enlarges it.

Player list:
- A long player name pushed that row's character and buttons to the
  right. Names now take the free space and shorten with an ellipsis, so
  all rows line up and use the full width of the panel.

winner_window.gd

@@ -1,4 +1,4 @@
-extends Control
+extends PopupWindow
 
 @onready
 var winner_panel: Panel = %WinnerPanel
@@ -23,6 +23,11 @@ func show_winner(winner: PlayerObject) -> void:
 	winner_label.text = winner.player_name + " won with " + str(winner.player_score) + \
 	" points!!"
 	winner_picture.texture = winner.character
+	# The "no character" placeholder is pixel art, which blurs when scaled up smoothly
+	if winner.character.resource_path == PlayerObject.NO_CHARACTER_PATH:
+		winner_picture.texture_filter = CanvasItem.TEXTURE_FILTER_NEAREST
+	else:
+		winner_picture.texture_filter = CanvasItem.TEXTURE_FILTER_LINEAR
 	winner_picture.custom_minimum_size = Vector2(480, 200)
 	winner_picture.expand_mode = TextureRect.EXPAND_FIT_WIDTH_PROPORTIONAL
 	winner_picture.stretch_mode = TextureRect.STRETCH_KEEP_ASPECT_CENTERED
@@ -50,13 +55,4 @@ func show_winner(winner: PlayerObject) -> void:
 		placing += 1
 
 
-func hide_window() -> void:
-	visible = false
 
-
-func _input(event: InputEvent) -> void:
-	if visible:
-		if event is InputEventMouseButton and event.is_pressed():
-			var ev_local: InputEvent = make_input_local(event)
-			if !Rect2(Vector2(0, 0), winner_panel.size).has_point(ev_local.position):
-				visible = false