Change soundtrack covers from the app and show the cover with the answer

Cover menu in the soundtrack popup ("Change cover"):
- Choose picture uploads a JPEG, PNG or WebP picture (up to 10 MB).
- Pick by ID uses a game's cover on SteamGridDB or an anime's on AniList.
- Remove cover deletes it, so the server searches for a new one.
- The server's reason is shown when it refuses a change.
After a change the new cover time is fetched, and the popup, the
statistics card and the quiz show the new cover.

Quiz: once the answer is shown, the soundtrack's cover shows to the left of
the titles. Cover and titles are centered together, left and right and up
and down, and each title keeps to two lines. Cover times come from the
soundtrack list, and songs keep their soundtrack's UUID, also in saves.

Requests can now send any body with its content type, and every 2xx answer
counts as success. Cover frames are 2:3 like the server's covers. Small
copies of real covers are used by the tests and screenshots.

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

statistics/SoundtrackCard.tscn

@@ -20,7 +20,7 @@ theme_override_constants/separation = 10
 [node name="CoverFrame" type="Panel" parent="VBox/Header"]
 unique_name_in_owner = true
 clip_children = 2
-custom_minimum_size = Vector2(72, 100)
+custom_minimum_size = Vector2(68, 102)
 layout_mode = 2
 mouse_filter = 2
 theme_type_variation = &"SoundtrackCover"

statistics/soundtrack_card.gd

@@ -80,6 +80,14 @@ func load_cover(covers: CoverCache) -> void:
 	covers.fetch_cover(soundtrack.soundtrack_uuid, soundtrack.cover_modified, show_cover)
 
 
+## Takes the soundtrack's new cover time [param modified], 0 when its cover was removed,
+## and shows the initials until [method load_cover] fetches the new cover.
+func set_cover_time(modified: int) -> void:
+	soundtrack.cover_modified = modified
+	show_cover(null)
+	_cover_asked = 0
+
+
 ## 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

statistics/statistics_view.gd

@@ -200,6 +200,15 @@ func update_alternative_names(updated: Soundtrack) -> void:
 	apply_filter()
 
 
+## Shows the new cover of the soundtrack [param uuid], with the cover time
+## [param modified], or its initials when [param modified] is 0.
+func update_cover(uuid: String, modified: int) -> void:
+	for card: SoundtrackCard in cards:
+		if card.soundtrack.soundtrack_uuid == uuid:
+			card.set_cover_time(modified)
+	load_covers_on_screen()
+
+
 func _update_search_names() -> void:
 	var names: Array[String] = []
 	var alternatives: Dictionary = {}