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>

data/settings.gd

@@ -6,6 +6,10 @@ extends Node
 ## Emitted when another theme is used, for code that reads theme colours itself.
 signal theme_changed
 
+## How the server picks a random song: any soundtrack then any of its songs, preferring
+## soundtracks played less than average, or every song with the same chance.
+enum RandomMode { NORMAL, LOW_PLAYED, CLASSIC }
+
 const MAX_NUMBER_OF_PLAYERS: int = 7
 ## How many letters a search needs before it also finds names with the letters in order
 ## but apart, e.g. "lttp" for "A Link to the Past". Shorter searches only find names
@@ -26,7 +30,7 @@ const SAVED_SETTINGS: Dictionary[String, Array] = {
 	"quiz": [
 		&"auto_repeat_song", &"stop_after_current", &"hide_next_track", &"hide_beginning",
 		&"hide_for_seconds", &"hide_length", &"hide_ticks", &"winning_score",
-		&"inspiration_list_speed",
+		&"inspiration_list_speed", &"short_songs", &"short_song_seconds",
 	],
 	"window": [&"fullscreen"],
 	"app": [&"last_seen_version", &"theme_id", &"reduce_animations"],
@@ -77,7 +81,8 @@ var stop_after_current: bool = true
 var auto_repeat_song: bool = true
 var hide_next_track: bool = true
 var add_to_stats: bool = true
-var use_low_played_mode: bool = false
+## How the server picks random songs. Not saved, like statistics counting.
+var random_mode: RandomMode = RandomMode.NORMAL
 var winning_score: int = 20
 var fullscreen: bool = false
 var inspiration_list_speed: int = 1
@@ -85,6 +90,10 @@ var hide_for_seconds: float = 5.0
 var hide_beginning: bool = false
 var hide_length: bool = false
 var hide_ticks: bool = false
+## Plays only [member short_song_seconds] of each song, from a random point, so more
+## songs fit in a game.
+var short_songs: bool = false
+var short_song_seconds: int = 30
 var player_array: Array[PlayerObject]
 var edit_players: bool = false
 var currently_syncing: bool = false

data/song_object.gd

@@ -17,6 +17,9 @@ var is_playing: bool = false
 var song_path: String = ""
 ## The song itself, only when it could not be saved to a file.
 var song: AudioStream
+## Where the part played with Short songs starts, in seconds, or -1 before it is picked.
+## Picked once, so restarting and repeating play the same part.
+var short_start: float = -1.0
 
 
 func get_soundtrack_title() -> String: