Add Short songs and a choice of how random songs are picked (#30, #51)

Short songs (#30): a quiz settings switch and a Seconds per song row (30 by
default, 10-120 in steps of 5), saved with the quiz settings. Only part of
each quiz song plays, from a random point 10-60% into it, picked once per song
so restart and repeat play the same part. The progress bar, time and seeking
stay within the part, a hidden beginning counts inside it, and its end counts
as the song ending (repeat, stop or go to the next song as set).

Random songs (#51): the low-played switch in Settings is now a Normal / Low
played / Classic choice, stored as Settings.random_mode and not saved.
fetch_random_song(mode) picks /music/rand, /music/rand/low or
/music/rand/classic.

Closes #30
Closes #51

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

popups/SettingsPopup.tscn

@@ -205,12 +205,31 @@ action_mode = 0
 theme_type_variation = &"StepButton"
 text = "+1"
 
-[node name="LowPlayedCheckButton" type="CheckButton" parent="SettingsPanel/VBoxContainer"]
-unique_name_in_owner = true
+[node name="RandomModeRow" type="HBoxContainer" parent="SettingsPanel/VBoxContainer"]
 layout_mode = 2
+
+[node name="Title" type="Label" parent="SettingsPanel/VBoxContainer/RandomModeRow"]
+layout_mode = 2
+size_flags_horizontal = 3
+theme_type_variation = &"SettingsRowLabel"
+text = "Random songs"
+
+[node name="RandomModeButton" type="OptionButton" parent="SettingsPanel/VBoxContainer/RandomModeRow"]
+unique_name_in_owner = true
+custom_minimum_size = Vector2(180, 0)
+layout_mode = 2
+tooltip_text = "Normal: a random soundtrack, then one of its songs.
+Low played: the same, but soundtracks played less than average come up more often.
+Classic: every song has the same chance, whatever its soundtrack."
 focus_mode = 0
-action_mode = 0
-text = "Prefer less played soundtracks"
+selected = 0
+item_count = 3
+popup/item_0/text = "Normal"
+popup/item_0/id = 0
+popup/item_1/text = "Low played"
+popup/item_1/id = 1
+popup/item_2/text = "Classic"
+popup/item_2/id = 2
 
 [node name="AddToDatabaseCheckButton" type="CheckButton" parent="SettingsPanel/VBoxContainer"]
 unique_name_in_owner = true

popups/settings_popup.gd

@@ -1,9 +1,9 @@
 class_name SettingsPopup
 extends BasePopup
 ## The application settings: which MusicServer or music folder to play from, the theme,
-## fullscreen, fewer animations, how many songs to download ahead, whether to prefer less played soundtracks
-## and whether plays count in the statistics, and a button that opens the folder the
-## settings are kept in. Opened from the Settings button in the top bar.
+## fullscreen, fewer animations, how many songs to download ahead, how random songs are
+## picked and whether plays count in the statistics, and a button that opens the folder
+## the settings are kept in. Opened from the Settings button in the top bar.
 ##
 ## A music folder (see [MusicFolder]) is used instead of the server until Use server is
 ## pressed or the game is closed. The settings that need the server are off meanwhile.
@@ -30,7 +30,7 @@ const PADDING: Vector2 = Vector2(20, 12)
 @onready var cache_label: Label = %CacheLabel
 @onready var lower_cache_button: Button = %LowerCacheButton
 @onready var increase_cache_button: Button = %IncreaseCacheButton
-@onready var low_played_button: CheckButton = %LowPlayedCheckButton
+@onready var random_mode_button: OptionButton = %RandomModeButton
 @onready var add_to_database_button: CheckButton = %AddToDatabaseCheckButton
 @onready var rows: VBoxContainer = %VBoxContainer
 @onready var folder_label: Label = %FolderLabel
@@ -81,8 +81,8 @@ func _ready() -> void:
 	lower_cache_button.pressed.connect(lower_cache)
 	increase_cache_button.pressed.connect(increase_cache)
 	select_server_button.item_selected.connect(select_server)
-	low_played_button.toggled.connect(
-			func(on: bool) -> void: Settings.use_low_played_mode = on)
+	random_mode_button.item_selected.connect(
+			func(mode: int) -> void: Settings.random_mode = mode as Settings.RandomMode)
 	add_to_database_button.toggled.connect(func(on: bool) -> void: Settings.add_to_stats = on)
 	visibility_changed.connect(_on_visibility_changed)
 	# Alt+Enter switches fullscreen from the main window, which resizes the window
@@ -189,7 +189,7 @@ func _use_server(new_server: int) -> void:
 func _on_visibility_changed() -> void:
 	if visible:
 		_update_fullscreen_button()
-		low_played_button.set_pressed_no_signal(Settings.use_low_played_mode)
+		random_mode_button.select(Settings.random_mode)
 		add_to_database_button.set_pressed_no_signal(Settings.add_to_stats)
 	else:
 		folder_error_label.visible = false
@@ -224,7 +224,7 @@ func _show_music_source() -> void:
 		characters_label.text = "From " + folder.display_name()
 	else:
 		characters_label.text = "From the server"
-	for control: BaseButton in [select_server_button, low_played_button, add_to_database_button]:
+	for control: BaseButton in [select_server_button, random_mode_button, add_to_database_button]:
 		control.disabled = folder != null
 	_fit_to_rows()