fix(mobile): apply useModalStyle to remaining dialog files (Bug #9)

Completes the mobile fullscreen modal pass — adds useModalStyle to
DeviceVerificationSetup, DeviceVerificationReset, AddExistingModal,
RoomEncryption prompt, RoomUpgradeDialog, Modal500, ReadReceiptAvatars,
and RoomTopicViewer. All floating Dialog/Modal components now go
fullscreen on mobile (≤750px). UIAFlowOverlay was already fullscreen
via <Overlay>; JoinRulesSwitcher/RoomNotificationSwitcher are dropdowns.

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

src/app/components/DeviceVerificationSetup.tsx

@@ -1,4 +1,5 @@
 import React, { FormEventHandler, forwardRef, useCallback, useState } from 'react';
+import { useModalStyle } from '../hooks/useModalStyle';
 import {
   Dialog,
   Header,
@@ -287,9 +288,10 @@ type DeviceVerificationSetupProps = {
 export const DeviceVerificationSetup = forwardRef<HTMLDivElement, DeviceVerificationSetupProps>(
   ({ onCancel }, ref) => {
     const [recoveryKey, setRecoveryKey] = useState<string>();
+    const modalStyle = useModalStyle(480);
 
     return (
-      <Dialog ref={ref}>
+      <Dialog ref={ref} style={modalStyle}>
         <Header
           style={{
             padding: `0 ${config.space.S200} 0 ${config.space.S400}`,
@@ -324,9 +326,10 @@ type DeviceVerificationResetProps = {
 export const DeviceVerificationReset = forwardRef<HTMLDivElement, DeviceVerificationResetProps>(
   ({ onCancel }, ref) => {
     const [reset, setReset] = useState(false);
+    const modalStyle = useModalStyle(480);
 
     return (
-      <Dialog ref={ref}>
+      <Dialog ref={ref} style={modalStyle}>
         <Header
           style={{
             padding: `0 ${config.space.S200} 0 ${config.space.S400}`,