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/SoundtrackCard.tscn

@@ -12,9 +12,52 @@ script = ExtResource("card_script")
 layout_mode = 2
 mouse_filter = 2
 
-[node name="NameLabel" type="Label" parent="VBox" unique_id=1211000003]
+[node name="Header" type="HBoxContainer" parent="VBox"]
+layout_mode = 2
+mouse_filter = 2
+theme_override_constants/separation = 10
+
+[node name="CoverFrame" type="Panel" parent="VBox/Header"]
 unique_name_in_owner = true
-custom_minimum_size = Vector2(0, 62)
+clip_children = 2
+custom_minimum_size = Vector2(72, 100)
+layout_mode = 2
+mouse_filter = 2
+theme_type_variation = &"SoundtrackCover"
+
+[node name="CoverPlaceholder" type="Label" parent="VBox/Header/CoverFrame"]
+unique_name_in_owner = true
+layout_mode = 1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+mouse_filter = 2
+theme_type_variation = &"TextLarge"
+horizontal_alignment = 1
+vertical_alignment = 1
+
+[node name="CoverPicture" type="TextureRect" parent="VBox/Header/CoverFrame"]
+unique_name_in_owner = true
+layout_mode = 1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+mouse_filter = 2
+expand_mode = 1
+stretch_mode = 6
+
+[node name="Info" type="VBoxContainer" parent="VBox/Header"]
+layout_mode = 2
+size_flags_horizontal = 3
+mouse_filter = 2
+
+[node name="NameLabel" type="Label" parent="VBox/Header/Info" unique_id=1211000003]
+unique_name_in_owner = true
+custom_minimum_size = Vector2(0, 50)
 layout_mode = 2
 mouse_filter = 2
 theme_type_variation = &"TextLarge"
@@ -22,12 +65,12 @@ autowrap_mode = 3
 text_overrun_behavior = 3
 max_lines_visible = 2
 
-[node name="PlayedLabel" type="Label" parent="VBox" unique_id=1211000004]
+[node name="PlayedLabel" type="Label" parent="VBox/Header/Info" unique_id=1211000004]
 unique_name_in_owner = true
 layout_mode = 2
 mouse_filter = 2
 
-[node name="LastPlayedLabel" type="Label" parent="VBox" unique_id=1211000005]
+[node name="LastPlayedLabel" type="Label" parent="VBox/Header/Info" unique_id=1211000005]
 unique_name_in_owner = true
 layout_mode = 2
 mouse_filter = 2