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/features/common-settings/general/RoomUpgrade.tsx

@@ -39,12 +39,14 @@ import { useAlive } from '../../../hooks/useAlive';
 import { creatorsSupported } from '../../../utils/matrix';
 import { useRoomCreators } from '../../../hooks/useRoomCreators';
 import { BreakWord } from '../../../styles/Text.css';
+import { useModalStyle } from '../../../hooks/useModalStyle';
 
 function RoomUpgradeDialog({ requestClose }: { requestClose: () => void }) {
   const mx = useMatrixClient();
   const room = useRoom();
   const alive = useAlive();
   const creators = useRoomCreators(room);
+  const modalStyle = useModalStyle(480);
 
   const capabilities = useCapabilities();
   const roomVersions = capabilities['m.room_versions'];
@@ -93,7 +95,7 @@ function RoomUpgradeDialog({ requestClose }: { requestClose: () => void }) {
             escapeDeactivates: stopPropagation,
           }}
         >
-          <Dialog variant="Surface">
+          <Dialog variant="Surface" style={modalStyle}>
             <Header
               style={{
                 padding: `0 ${config.space.S200} 0 ${config.space.S400}`,