Add animations to popups, points, songs, the winner and the tabs (#48)

Popups fade in while growing and close the reverse way, with the backdrop
fading along. The winner gets confetti, bouncing pictures and a score graph
that draws itself from the left. Filtered statistics cards and search rows
fade in, the tabs slide in from their side, and every button bounces on hover
and click (ButtonBounce, now added to all buttons).

In the player list the score pops on every point, the first point flashes the
row, and a player on match point glows with a "Match point!" tag. A song
starting fades in the title, flashes its row (kept across list rebuilds) and
pops the play button.

Common/anim.gd holds the helpers. A saved "Reduce animations" switch in
Settings turns all movement off; the tests use it. The flash colours are
theme colours (Palette first_point, match_point, flash) in every theme.

Closes #48

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

data/settings.gd

@@ -29,7 +29,7 @@ const SAVED_SETTINGS: Dictionary[String, Array] = {
 		&"inspiration_list_speed",
 	],
 	"window": [&"fullscreen"],
-	"app": [&"last_seen_version", &"theme_id"],
+	"app": [&"last_seen_version", &"theme_id", &"reduce_animations"],
 }
 ## The looks the game can have, picked in Settings: an id that is saved, the name shown
 ## and the theme file. The first is the default. See themes/README.md.
@@ -96,6 +96,8 @@ var queue_ids: Dictionary[String, String] = {}
 ## The version the game last showed the About popup for. When it is not [member version],
 ## this version is new and the main window opens the About popup to show what is new.
 var last_seen_version: String = ""
+## Turns every animation off, so nothing moves. See [Anim].
+var reduce_animations: bool = false
 ## The id of the theme in use, one of [constant THEMES].
 var theme_id: String = THEMES[0].id
 ## The folder songs are played from instead of the server, picked in the settings, or null