DP16: add typed get/setAccountData helpers, remove ~19 any-casts

Add centralized typed helpers in src/app/utils/accountData.ts:
- getAccountData<T>(mx, eventType): T | undefined (returns content)
- setAccountData<T>(mx, eventType, content): Promise<void>

These wrap the single `as any` cast needed because matrix-js-sdk's typed
overloads reject the fork's custom account-data event names. Every call site
now stays fully typed on its content shape.

Route all account-data reads/writes that previously used
`(mx as any).getAccountData/setAccountData` or `mx.getAccountData(... as any)`
through the helpers (or, where a MatrixEvent is needed, through the existing
utils/room.ts getAccountData whose param is widened to accept string keys).
No behavior change: same event types, same content shapes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/room-nav/RoomNavItem.tsx

@@ -34,6 +34,7 @@ import { NavItem, NavItemContent, NavItemOptions, NavLink } from '../../componen
 import { UnreadBadge, UnreadBadgeCenter } from '../../components/unread-badge';
 import { RoomAvatar, RoomIcon } from '../../components/room-avatar';
 import { getDirectRoomAvatarUrl, getRoomAvatarUrl, getStateEvent } from '../../utils/room';
+import { setAccountData } from '../../utils/accountData';
 import { nameInitials } from '../../utils/common';
 import { useMatrixClient } from '../../hooks/useMatrixClient';
 import { useRoomUnread } from '../../state/hooks/unread';
@@ -127,11 +128,9 @@ function RenameRoomDialog({ room, onClose }: RenameRoomDialogProps) {
     const existing = getLocalRoomNamesContent(mx);
     if (newName === '') {
       const { [room.roomId]: _removed, ...rest } = existing.rooms;
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (mx as any).setAccountData(LOCAL_ROOM_NAMES_KEY, { rooms: rest });
+      setAccountData(mx, LOCAL_ROOM_NAMES_KEY, { rooms: rest });
     } else {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (mx as any).setAccountData(LOCAL_ROOM_NAMES_KEY, {
+      setAccountData(mx, LOCAL_ROOM_NAMES_KEY, {
         rooms: { ...existing.rooms, [room.roomId]: newName },
       });
     }
@@ -141,8 +140,7 @@ function RenameRoomDialog({ room, onClose }: RenameRoomDialogProps) {
   const handleClear = useCallback(() => {
     const existing = getLocalRoomNamesContent(mx);
     const { [room.roomId]: _removed, ...rest } = existing.rooms;
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    (mx as any).setAccountData(LOCAL_ROOM_NAMES_KEY, { rooms: rest });
+    setAccountData(mx, LOCAL_ROOM_NAMES_KEY, { rooms: rest });
     onClose();
   }, [mx, room.roomId, onClose]);