Add a Statistics tab with a card for every soundtrack

Part of #41. The top bar has Quiz and Statistics tabs instead of the
Statistics button. The Statistics tab replaces the quiz below the top bar
(the song keeps playing) and shows every soundtrack as a card with its
plays, last played date and most and least played songs, loaded from the
new GET /api/v1/statistics/soundtracks. The cards can be searched (with
the Search popup's matching, now in SoundtrackSearch), filtered on played
or never played, and sorted A-Z, Z-A, most or least played. Clicking a
card opens a popup with all its songs.

Screenshots of the other states only differ in the top bar, and the
layout baseline is taken again with the new statistics states.

tests/unit/test_music_server_client.gd

@@ -410,6 +410,8 @@ func test_endpoint_paths_and_methods() -> void:
 				"/download/linux", HTTPClient.METHOD_GET],
 		[func() -> void: MusicServerClient.cleanup_tokens(noop),
 				"/token/cleanup", HTTPClient.METHOD_POST],
+		[func() -> void: MusicServerClient.fetch_soundtrack_statistics(noop),
+				"/statistics/soundtracks", HTTPClient.METHOD_GET],
 		[func() -> void: MusicServerClient.fetch_statistics_summary(noop),
 				"/statistics/summary", HTTPClient.METHOD_GET],
 		[func() -> void: MusicServerClient.fetch_most_played_soundtracks(5, noop),
@@ -467,6 +469,22 @@ func test_most_played_soundtracks_are_typed_with_their_songs() -> void:
 	assert_array(received[1].songs).is_empty()
 
 
+func test_soundtrack_statistics_are_typed() -> void:
+	_server.respond_json("/statistics/soundtracks", [
+		{"soundtrack_name": "Chrono Trigger", "soundtrack_played": 2,
+				"songs": [{"song_name": "Frog's Theme", "times_played": 2}]},
+		{"soundtrack_name": "Lufia II", "soundtrack_played": 0, "songs": []},
+	])
+	var received: Array[SoundtrackWithSongs] = []
+
+	MusicServerClient.fetch_soundtrack_statistics(
+			func(list: Array[SoundtrackWithSongs]) -> void: received.append_array(list))
+
+	assert_int(received.size()).is_equal(2)
+	assert_str(received[0].songs[0].song_name).is_equal("Frog's Theme")
+	assert_int(received[1].soundtrack_played).is_equal(0)
+
+
 func test_most_played_songs_are_typed() -> void:
 	_server.respond_json("/statistics/songs/most-played?limit=1", [
 		{"song_uuid": "so-1", "song_name": "Dancing Mad", "times_played": 12},
@@ -484,7 +502,7 @@ func test_statistics_calls_on_failed_on_server_error() -> void:
 	var outcome: Array[String] = []
 	var on_done: Callable = func(_data: Variant) -> void: outcome.append("done")
 	var on_failed: Callable = func() -> void: outcome.append("failed")
-	for path: String in ["/statistics/summary",
+	for path: String in ["/statistics/summary", "/statistics/soundtracks",
 			"/statistics/soundtracks/most-played?limit=3",
 			"/statistics/soundtracks/least-played?limit=3",
 			"/statistics/soundtracks/last-played?limit=3",
@@ -497,7 +515,7 @@ func test_statistics_calls_on_failed_on_server_error() -> void:
 	_call_every_statistics_endpoint(on_done, on_failed)
 
 	assert_array(outcome).contains_exactly(["failed", "failed", "failed", "failed", "failed",
-			"failed", "failed", "failed"])
+			"failed", "failed", "failed", "failed"])
 
 
 func test_statistics_calls_on_failed_when_token_is_refused() -> void:
@@ -509,11 +527,12 @@ func test_statistics_calls_on_failed_when_token_is_refused() -> void:
 
 	assert_array(_server.requested_paths).is_empty()
 	assert_array(outcome).contains_exactly(["failed", "failed", "failed", "failed", "failed",
-			"failed", "failed", "failed"])
+			"failed", "failed", "failed", "failed"])
 
 
 func _call_every_statistics_endpoint(on_done: Callable, on_failed: Callable) -> void:
 	MusicServerClient.fetch_statistics_summary(on_done, on_failed)
+	MusicServerClient.fetch_soundtrack_statistics(on_done, on_failed)
 	MusicServerClient.fetch_most_played_soundtracks(3, on_done, on_failed)
 	MusicServerClient.fetch_least_played_soundtracks(3, on_done, on_failed)
 	MusicServerClient.fetch_last_played_soundtracks(3, on_done, on_failed)