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/add-existing/AddExisting.tsx

@@ -54,6 +54,7 @@ import { StateEvent } from '../../../types/matrix/room';
 import { getViaServers } from '../../plugins/via-servers';
 import { rateLimitedActions } from '../../utils/matrix';
 import { useAlive } from '../../hooks/useAlive';
+import { useModalStyle } from '../../hooks/useModalStyle';
 
 const SEARCH_OPTS: UseAsyncSearchOptions = {
   limit: 500,
@@ -72,6 +73,7 @@ type AddExistingModalProps = {
 };
 export function AddExistingModal({ parentId, space, requestClose }: AddExistingModalProps) {
   const mx = useMatrixClient();
+  const modalStyle = useModalStyle(480);
   const useAuthentication = useMediaAuthentication();
   const alive = useAlive();
 
@@ -188,7 +190,7 @@ export function AddExistingModal({ parentId, space, requestClose }: AddExistingM
             escapeDeactivates: stopPropagation,
           }}
         >
-          <Modal size="300">
+          <Modal size="300" style={modalStyle}>
             <Box grow="Yes" direction="Column">
               <Header
                 size="500"

src/app/features/common-settings/general/RoomEncryption.tsx

@@ -28,6 +28,7 @@ import { useRoom } from '../../../hooks/useRoom';
 import { useStateEvent } from '../../../hooks/useStateEvent';
 import { stopPropagation } from '../../../utils/keyboard';
 import { RoomPermissionsAPI } from '../../../hooks/useRoomPermissions';
+import { useModalStyle } from '../../../hooks/useModalStyle';
 
 const ROOM_ENC_ALGO = 'm.megolm.v1.aes-sha2';
 
@@ -37,6 +38,7 @@ type RoomEncryptionProps = {
 export function RoomEncryption({ permissions }: RoomEncryptionProps) {
   const mx = useMatrixClient();
   const room = useRoom();
+  const modalStyle = useModalStyle(480);
 
   const canEnable = permissions.stateEvent(StateEvent.RoomEncryption, mx.getSafeUserId());
   const content = useStateEvent(room, StateEvent.RoomEncryption)?.getContent<{
@@ -111,7 +113,7 @@ export function RoomEncryption({ permissions }: RoomEncryptionProps) {
                   escapeDeactivates: stopPropagation,
                 }}
               >
-                <Dialog variant="Surface">
+                <Dialog variant="Surface" style={modalStyle}>
                   <Header
                     style={{
                       padding: `0 ${config.space.S200} 0 ${config.space.S400}`,

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}`,