fix(ui): lower-overhead Reduced effects for constrained GPUs (#1616)

* fix(ui): lower-overhead Reduced effects path for constrained GPUs

Disable backdrop-filter glass and solidify chrome fills when data-effects is reduced (Calm default), with Appearance warning and docs for constrained rendering devices. Related to #1614.

* test(ui): harden Reduced effects glass e2e and docs wording

Parse Color Level 4 slash alpha so opacity asserts are not vacuously true, cover dialog/toast/overlay both ways with stable data-sn hooks, and soften troubleshooting copy that overstated the unmeasured diagnosis.

* docs(ui): lead constrained-GPU guidance with Reduced Motion

Rename the troubleshooting section to neutral GPU framing, point Appearance and docs at Reduced Motion first, and show the callout whenever Motion is off so Calm or Reduced effects alone do not hide the validated workaround.

frontend/src/components/DeployFeedbackPill.tsx

@@ -41,6 +41,7 @@ function DeployFeedbackPillBase({ isVisible, onExpand }: DeployFeedbackPillProps
       onClick={onExpand}
       onKeyDown={handleKeyDown}
       className="fixed bottom-6 left-1/2 -translate-x-1/2 z-50 w-[280px] bg-popover/95 backdrop-blur-[10px] backdrop-saturate-[1.15] border border-glass-border rounded-full px-3 py-1.5 shadow-lg cursor-pointer flex items-center gap-2 max-md:bottom-[calc(var(--sn-mobile-tabbar-h)_+_env(safe-area-inset-bottom)_+_0.75rem)]"
+      data-sn-glass="panel"
     >
       <span className={dotClass} />
       <span className={cn(textClass, 'flex items-center gap-1 min-w-0 flex-1 overflow-hidden')}>