Show soundtrack covers and edit alternative names (#49)

Covers: statistics cards show the soundtrack's cover on the left, and the
statistics popup shows it large. Until it arrives, and without a cover, the
soundtrack's initials stand in. Covers load only for cards on or near the
screen, three at a time, and are cached in covers/ next to the settings
(CoverCache), downloaded again only when cover_modified changes. The index and
file handling are shared with CharacterCache in a new FileCache.

Alternative names: the popup shows them and has an editor (add, remove, save)
that sends PUT /soundtracks/{uuid}/alternative-names. The statistics search and
the Search popup find soundtracks by them; Search shows the matching name after
the real one. Search now loads /soundtracks, falling back to the plain list.

The API types are regenerated from the server's spec, with a SoundtrackCover
theme style in every theme.

Closes #49

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

statistics/soundtrack_card.gd

@@ -4,6 +4,9 @@ extends PanelContainer
 ## played, and its most and least played songs. Songs never played are not listed, and
 ## the least played are only shown when there are enough played songs to not repeat
 ## any. Clicking it asks for all its songs.
+##
+## Its cover shows on the left once [method load_cover] has fetched it; until then, and
+## when the soundtrack has no cover, the soundtrack's initials stand in for it.
 
 ## Emitted when the card is clicked.
 signal pressed(soundtrack: SoundtrackWithSongs)
@@ -15,6 +18,11 @@ const SONGS_SHOWN: int = 3
 ## The soundtrack the card shows.
 var soundtrack: SoundtrackWithSongs
 
+# The cover time asked for, so a cover is only asked for again when it changed
+var _cover_asked: int = 0
+
+@onready var cover_picture: TextureRect = %CoverPicture
+@onready var cover_placeholder: Label = %CoverPlaceholder
 @onready var name_label: Label = %NameLabel
 @onready var played_label: Label = %PlayedLabel
 @onready var last_played_label: Label = %LastPlayedLabel
@@ -32,7 +40,14 @@ func _ready() -> void:
 
 ## Shows [param data] on the card.
 func show_soundtrack(data: SoundtrackWithSongs) -> void:
+	var cover_changed: bool = soundtrack == null \
+			|| soundtrack.soundtrack_uuid != data.soundtrack_uuid \
+			|| soundtrack.cover_modified != data.cover_modified
 	soundtrack = data
+	if cover_changed:
+		show_cover(null)
+		_cover_asked = 0
+	cover_placeholder.text = initials(data.soundtrack_name)
 	name_label.text = data.soundtrack_name
 	tooltip_text = data.soundtrack_name
 	played_label.text = played_text(data.soundtrack_played)
@@ -55,6 +70,34 @@ func show_soundtrack(data: SoundtrackWithSongs) -> void:
 	_fill_song_list(least_played_list, least_played)
 
 
+## Asks [param covers] for the soundtrack's cover, unless it already has, and shows it
+## when it comes. Soundtracks without a cover keep their initials.
+func load_cover(covers: CoverCache) -> void:
+	if soundtrack == null || soundtrack.cover_modified <= 0 \
+			|| _cover_asked == soundtrack.cover_modified:
+		return
+	_cover_asked = soundtrack.cover_modified
+	covers.fetch_cover(soundtrack.soundtrack_uuid, soundtrack.cover_modified, show_cover)
+
+
+## Shows [param cover], or the initials when it is null.
+func show_cover(cover: Image) -> void:
+	cover_picture.texture = ImageTexture.create_from_image(cover) if cover != null else null
+	cover_placeholder.visible = cover == null
+
+
+## Up to two initials of [param soundtrack_name], e.g. "FF" for "Final Fantasy VI".
+static func initials(soundtrack_name: String) -> String:
+	var letters: String = ""
+	for word: String in soundtrack_name.split(" ", false):
+		var first: String = word.left(1)
+		if first.to_upper() != first.to_lower():
+			letters += first.to_upper()
+		if letters.length() == 2:
+			break
+	return letters if !letters.is_empty() else soundtrack_name.left(1)
+
+
 ## "Played 3 times", or "Never played" for [code]0[/code].
 static func played_text(times_played: int) -> String:
 	if times_played == 0: