feat(shell): app-wide dynamic album-art background ("modo Cider")
Opt-in album-art background composited behind the whole shell, wgpu-tier
only. Appearance mode picker: Off | Ambient (GPU shader) | Blurred art.
- ambient.wgsl: new calm, low-energy album-colored scene (mode 7), drifting
mesh-gradient of the primary/secondary/accent triad, no beat/transient.
Registered in shader_underlay SHADER_SOURCES[5] + render_frame idx math.
- state.slint: AppearanceState app-background {modes,mode-index,available,
dim,surface-alpha}; ImmersiveState.app-shader-mode (derived 1->7);
ShellState.app-background-active (mode>0 && wgpu && has-track).
- visualizer.rs: drain renders shader-mode when immersive OPEN, else
app-shader-mode (7=ambient) into the same shader-texture sink.
- AppShell: background layer at root z-bottom (Ambient=shader texture,
Blurred=ImmersiveAtmosphere) + tunable dark scrim; shell chrome surfaces
go translucent when active; viz-should-run extended to drive the drain.
- Whole-shell translucency: Sidebar/HeaderBar/PlayerBar(Small)/QueueSidebar/
LyricsSidebar/SidebarNowPlayingDock + AppShell content well/frame/column.
- ui_prefs: persisted `app_background` (off|ambient|blurred), String-key
pattern; appearance-select("app-background") write-back.
- Live-tunable knobs QBZ_BG_DIM / QBZ_BG_SURFACE_ALPHA (seeded at startup)
so the look is dialed in one smoke session without a rebuild.
- i18n: 8 locales for the picker + warning; reduce-motion / D4 (no-track ->
opaque theme) handled via derived active flag.
Design + signed decisions: qbz-nix-docs/specs/2026-07-16-app-wide-dynamic-background.md
cc
vicrodh
76ea5a82bb