Add a no-animations mode, on by default in VMs (#13550)

A machine without a GPU, like most VMs, renders through llvmpipe on the
CPU, where every animated frame and every translucent window costs. In a
VM, opening and closing a terminal took ~5s of CPU; a panel ~3.4s.

omarchy toggle animations (also under Toggle > Animations) places a Hyprland
flag that turns off animations, blur and shadows and makes windows opaque.
The shell follows Hyprland's animations:enabled, rereading it on every
config reload: its one-shot animations run for Style.duration(ms), which
is then 0, and its spinners, pulses and title marquee hold still. A new
install in a VM starts with the flag in place.

Measured in the ISO test VM (llvmpipe), CPU per interaction:
terminal open+close 5000ms -> 481ms, workspace switch 1670ms -> 409ms,
audio panel 3446ms -> 796ms, volume OSD 2324ms -> 584ms, menu 2028ms ->
1241ms.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

shell/Ui/Button.qml

@@ -125,7 +125,7 @@ BorderSurface {
   // dedicated selected border.
   borderSpec: _borderSpec
 
-  Behavior on color { ColorAnimation { duration: 120 } }
+  Behavior on color { ColorAnimation { duration: Style.duration(120) } }
 
   ToolTip {
     visible: root.tooltipText !== "" && mouseArea.containsMouse
@@ -174,7 +174,7 @@ BorderSurface {
         to: 360
         duration: 900
         loops: Animation.Infinite
-        running: root.iconSpinning
+        running: root.iconSpinning && !Style.reduceMotion
       }
     }