feat(sound): album art as the OSD background

When the current track has art, the volume OSD now draws it across the
whole panel, blurred (MultiEffect blur 0.5, default blurMax) and masked
to the panel's rounded corners, since clip only cuts to the bounding box.
The thumbnail in the track row stays sharp on top.

A dark scrim (Theme.base at 0.82) sits over the art. The palette is dark
and the text light, so a light cover made the panel unreadable, and more
blur did not fix that; only darkening did. The scrim is a sibling of the
MultiEffect, not a child: nested inside it, it did not paint at all, which
is why raising its alpha first appeared to change nothing.

Without art the panel keeps its translucent, compositor-frosted look.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/desktop/modules/sound/README.md b/desktop/modules/sound/README.md
index 72db235..d92d017 100644
--- a/desktop/modules/sound/README.md
+++ b/desktop/modules/sound/README.md
@@ -40,6 +40,12 @@ art, title, artist, and prev/play/next. With no player the panel is exactly
 the volume OSD, at its original size. A track change or a play/pause shows the
 panel too, so the row is not something you only see by touching the volume.
 
+When the track has art, it also fills the whole panel as a blurred background
+under a dark scrim (`Theme.base` at 0.82), and the thumbnail stays sharp in
+the row. The palette is dark, so the scrim is what keeps text legible on a
+light cover; blur alone did not. The art is opaque, so it hides the
+compositor's frosting while it shows. Without art the panel is unchanged.
+
 Hovering the panel freezes its fade so the buttons can be clicked; moving away
 starts the countdown again. Without a hover it behaves exactly as it did before
 there was anything clickable on it. It still takes no keyboard focus.