Give the sync progress bar colour and animation

The bar in the Sync popup is now an AnimatedProgressBar: taller, with a
darker track and the theme's accent fill (orange, frost blue in Nord, green
with a gold shine for Christmas). It shows Godot's busy animation until the
server reports progress, glides to each new value, has a soft highlight
sweeping along the filled part inside its rounded corners, and fills and
pops before the result shows. With Reduce animations it only jumps to its
values.

The styles are SyncProgressBar, SyncProgressBarFill and SyncProgressBarText
in every theme. Anim.stop stops a keyed animation without starting an empty
one.

The server now sends sync times as "MM:SS"; the spec is updated from
MusicServer develop (also the linux-package route), and the test data and
screenshots use the new format.

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

common/anim.gd

@@ -24,15 +24,20 @@ static func enabled() -> bool:
 ## one with the same key so they don't fight. Returns null when animations are off or the
 ## node is not in the tree.
 static func tween(node: Node, key: StringName = &"anim") -> Tween:
+	stop(node, key)
+	if !enabled() || !node.is_inside_tree():
+		return null
+	var new_tween: Tween = node.create_tween()
+	node.set_meta(StringName("_tween_" + key), new_tween)
+	return new_tween
+
+
+## Stops the animation called [param key] on [param node], if one is running.
+static func stop(node: Node, key: StringName = &"anim") -> void:
 	var meta: StringName = StringName("_tween_" + key)
 	var old: Variant = node.get_meta(meta) if node.has_meta(meta) else null
 	if old is Tween && (old as Tween).is_valid():
 		(old as Tween).kill()
-	if !enabled() || !node.is_inside_tree():
-		return null
-	var new_tween: Tween = node.create_tween()
-	node.set_meta(meta, new_tween)
-	return new_tween
 
 
 ## Makes [param control] grow from its middle.