fix(mobile): useModalStyle on 3 more dialogs, GPU hint animated bg, document untested fixes

- DeviceVerification, InviteUserPrompt, LogoutDialog: apply useModalStyle for
  fullscreen on mobile, capped box on desktop
- chatBackground: inject willChange + contain:paint on animated variants to
  promote compositor layer and prevent descendant repaint flickering (Bug #2)
- LOTUS_BUGS.md: mark #7-#10 FIXED/UNTESTED, #2 FIXED/UNTESTED, chatBackground
  backgroundColor values as PATTERN CONTENT EXCEPTION

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/components/DeviceVerification.tsx

@@ -30,6 +30,7 @@ import {
 } from '../hooks/useVerificationRequest';
 import { AsyncStatus, useAsyncCallback } from '../hooks/useAsyncCallback';
 import { ContainerColor } from '../styles/ContainerColor.css';
+import { useModalStyle } from '../hooks/useModalStyle';
 
 const DialogHeaderStyles: CSSProperties = {
   padding: `0 ${config.space.S200} 0 ${config.space.S400}`,
@@ -232,6 +233,7 @@ type DeviceVerificationProps = {
 };
 export function DeviceVerification({ request, onExit }: DeviceVerificationProps) {
   const phase = useVerificationRequestPhase(request);
+  const modalStyle = useModalStyle(480);
 
   const handleCancel = useCallback(() => {
     if (request.phase !== VerificationPhase.Done && request.phase !== VerificationPhase.Cancelled) {
@@ -255,7 +257,7 @@ export function DeviceVerification({ request, onExit }: DeviceVerificationProps)
             escapeDeactivates: false,
           }}
         >
-          <Dialog variant="Surface">
+          <Dialog variant="Surface" style={modalStyle}>
             <Header style={DialogHeaderStyles} variant="Surface" size="500">
               <Box grow="Yes">
                 <Text as="h2" size="H4">