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/FleetView/ReconnectingOverlay.tsx

@@ -55,7 +55,7 @@ export function ReconnectingOverlay({ preUpdateStartedAt }: ReconnectingOverlayP
     }, [timedOut, preUpdateStartedAt]);
 
     return (
-        <div className="fixed inset-0 z-50 flex items-center justify-center bg-background/80 backdrop-blur-[10px] backdrop-saturate-[1.15]">
+        <div className="fixed inset-0 z-50 flex items-center justify-center bg-background/80 backdrop-blur-[10px] backdrop-saturate-[1.15]" data-sn-glass="overlay">
             <div className="text-center space-y-4">
                 {timedOut ? (
                     <>

frontend/src/components/FleetView/UpdateStatusBadge.tsx

@@ -53,7 +53,7 @@ export function UpdateStatusBadge({ status, error, onRetry, onDismiss }: UpdateS
                                 <div className="h-2 w-2 rounded-full bg-destructive/60" />
                             </Cursor>
                             <CursorFollow side="bottom" sideOffset={8} align="end">
-                                <div className="bg-popover/95 backdrop-blur-[10px] backdrop-saturate-[1.15] border border-card-border shadow-md rounded-lg px-3 py-2 max-w-xs">
+                                <div className="bg-popover/95 backdrop-blur-[10px] backdrop-saturate-[1.15] border border-card-border shadow-md rounded-lg px-3 py-2 max-w-xs" data-sn-glass="panel">
                                     <p className="font-mono tabular-nums text-xs text-stat-subtitle">{error}</p>
                                 </div>
                             </CursorFollow>