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/hooks/useRoomMeta.ts

@@ -4,6 +4,7 @@ import { ClientEvent, MatrixEvent, Room, RoomEvent, RoomEventHandlerMap } from '
 import { StateEvent } from '../../types/matrix/room';
 import { useStateEvent } from './useStateEvent';
 import { useMatrixClient } from './useMatrixClient';
+import { getAccountData } from '../utils/accountData';
 
 export const useRoomAvatar = (room: Room, dm?: boolean): string | undefined => {
   const avatarEvent = useStateEvent(room, StateEvent.RoomAvatar);
@@ -42,9 +43,7 @@ export type LocalRoomNamesContent = { rooms: Record<string, string> };
 export function getLocalRoomNamesContent(
   mx: ReturnType<typeof useMatrixClient>,
 ): LocalRoomNamesContent {
-  // Use any-cast because LOCAL_ROOM_NAMES_KEY is not in matrix-js-sdk AccountDataEvents
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  const raw: unknown = (mx as any).getAccountData(LOCAL_ROOM_NAMES_KEY)?.getContent();
+  const raw: unknown = getAccountData<unknown>(mx, LOCAL_ROOM_NAMES_KEY);
   if (
     raw &&
     typeof raw === 'object' &&