Follow the GDScript style guide in every script

- Types on every parameter, return value and variable, and snake_case names
  (the player name limit is the constant MAX_NAME_LENGTH).
- Spelling fixes: *_triggered, character_selected, separator, caught_errors.
  The server's catched_errors key stays as the server sends it.
- Signals are connected with signal.connect() instead of by name.
- Code is ordered signals, constants, exported vars, vars, @onready vars,
  functions, with @onready on one line and two blank lines between functions.
- Every script starts with a ## description. Template comments, old LOC notes
  and commented-out code are gone, apart from the local play code.
- Lines are at most 100 characters, apart from the local play path.
- The screenshot tour turns off the blinking text cursor so pictures match.

main_window.gd

@@ -5,39 +5,20 @@ extends Control
 ## Everything that is not part of a quiz lives here, so other views can be added next
 ## to the quiz later.
 
-@onready
-var top_bar: TopBar = $TopBar
-
-@onready
-var quiz: Quiz = $Quiz
-
-@onready
-var search_popup: SearchPopup = $SearchPopup
-
-@onready
-var sync_popup: SyncPopup = %SyncPopup
-
-@onready
-var shortcuts_popup: ShortcutsPopup = %ShortcutsPopup
-
-@onready
-var qr_popup: QRPopup = %QRPopup
-
-@onready
-var about_popup: AboutPopup = %AboutPopup
-
-@onready
-var log_popup: LogPopup = %LogPopup
-
-@onready
-var statistic_popup: PopupPanel = $StatisticsPopupPanel
-
-@onready
-var statistic_label: Label = %StatisticsLabel
-
 ## Dims the window behind an open popup and keeps clicks from reaching the buttons under it.
 var popup_backdrop: PopupBackdrop
 
+@onready var top_bar: TopBar = $TopBar
+@onready var quiz: Quiz = $Quiz
+@onready var search_popup: SearchPopup = $SearchPopup
+@onready var sync_popup: SyncPopup = %SyncPopup
+@onready var shortcuts_popup: ShortcutsPopup = %ShortcutsPopup
+@onready var qr_popup: QRPopup = %QRPopup
+@onready var about_popup: AboutPopup = %AboutPopup
+@onready var log_popup: LogPopup = %LogPopup
+@onready var statistic_popup: PopupPanel = $StatisticsPopupPanel
+@onready var statistic_label: Label = %StatisticsLabel
+
 
 func _ready() -> void:
 	popup_backdrop = PopupBackdrop.add_to(self, _popups())
@@ -50,8 +31,8 @@ func _ready() -> void:
 	top_bar.about_pressed.connect(show_about)
 	top_bar.qr_pressed.connect(show_qr)
 
-	sync_popup.connect("sync_started", _on_sync_started)
-	sync_popup.connect("sync_finished", _on_sync_finished)
+	sync_popup.sync_started.connect(_on_sync_started)
+	sync_popup.sync_finished.connect(_on_sync_finished)
 	quiz.server_changed.connect(search_popup.get_list_of_soundtracks)
 	quiz.event_logged.connect(log_popup.add_log_row)
 
@@ -63,9 +44,9 @@ func _input(event: InputEvent) -> void:
 		if event.alt_pressed && event.keycode == KEY_ENTER:
 			GameLog.debug("Alt + Enter pressed")
 			Settings.fullscreen = !Settings.fullscreen
-			if Settings.fullscreen == true:
+			if Settings.fullscreen:
 				DisplayServer.window_set_mode(DisplayServer.WINDOW_MODE_FULLSCREEN)
-			if Settings.fullscreen == false:
+			if !Settings.fullscreen:
 				DisplayServer.window_set_mode(DisplayServer.WINDOW_MODE_WINDOWED)
 		if event.alt_pressed && event.keycode == KEY_K:
 			shortcuts_popup.toggle()