Split settings into a quiz card and an application Settings popup

- A Quiz settings button under the player bar opens a small card above
  it with the quiz settings, including Auto repeat, which moves there
  from under the player bar. The card does not dim the quiz, so it can
  be changed during a song, and grows to fit its rows.
- A Settings button in the top bar opens the application settings:
  server, fullscreen and songs to download ahead. Quick sync is gone,
  as the server no longer has it, and the server list is in Settings.
- Labels use sentence case, and seconds to hide show as whole numbers.
- Debug builds switch to the local server and a low winning score in
  the Settings autoload, before any scene asks the server for anything.
  The DEBUG label moves to the top bar, so it shows on every tab.
- Search moves from the top bar back to the quiz toolbar, as the
  Statistics tab has its own search.

main/main_window.gd

@@ -16,6 +16,7 @@ var popup_backdrop: PopupBackdrop
 @onready var qr_popup: QRPopup = %QRPopup
 @onready var about_popup: AboutPopup = %AboutPopup
 @onready var log_popup: LogPopup = %LogPopup
+@onready var settings_popup: SettingsPopup = %SettingsPopup
 @onready var statistics_view: StatisticsView = $StatisticsView
 @onready var soundtrack_stats_popup: SoundtrackStatsPopup = $SoundtrackStatsPopup
 
@@ -24,12 +25,15 @@ func _ready() -> void:
 	popup_backdrop = PopupBackdrop.add_to(self, _popups())
 	if OS.has_feature("macos"):
 		GameLog.debug("is_mac")
-	top_bar.search_pressed.connect(show_search)
+	quiz.search_pressed.connect(show_search)
 	top_bar.sync_pressed.connect(sync_soundtracks)
 	top_bar.tab_selected.connect(show_tab)
 	top_bar.shortcuts_pressed.connect(show_shortcuts)
 	top_bar.about_pressed.connect(show_about)
 	top_bar.qr_pressed.connect(show_qr)
+	top_bar.settings_pressed.connect(settings_popup.open)
+	settings_popup.server_changed.connect(quiz.on_server_changed)
+	settings_popup.visibility_changed.connect(_on_settings_popup_visibility_changed)
 
 	sync_popup.sync_started.connect(_on_sync_started)
 	sync_popup.sync_finished.connect(_on_sync_finished)
@@ -57,7 +61,14 @@ func _input(event: InputEvent) -> void:
 
 func _popups() -> Array[BasePopup]:
 	return [search_popup, sync_popup, qr_popup, shortcuts_popup, about_popup, log_popup,
-			soundtrack_stats_popup]
+			soundtrack_stats_popup, settings_popup]
+
+
+# How many songs to download ahead can be changed in the settings. Waiting until the
+# settings are closed avoids starting downloads while the number is clicked up and down.
+func _on_settings_popup_visibility_changed() -> void:
+	if !settings_popup.visible:
+		quiz.song_loader.fill_cache()
 
 
 func show_search() -> void: