refactor(DP15): centralize sendStateEvent as-any cast in typed helper

Add a typed `sendStateEvent(mx, roomId, eventType, content, stateKey?)`
helper in utils/room.ts that mirrors the DP16 account-data helper pattern.
The SDK's typed `sendStateEvent` overload rejects the fork's custom
`StateEvent` enum values, so every call site cast arg 2 to `any` (which
also collapsed the content type). The single `as any` cast now lives inside
the helper; a generic `content: T extends object` keeps each call site's
content type checked.

Route all 32 `mx.sendStateEvent(..., StateEvent.X as any, ...)` casts across
20 files through the helper. The 2 dynamic-string casts in developer-tools
(SendRoomEvent, StateEventEditor) pass a runtime string, not an enum value,
so they stay as-is.

No behavior change.

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

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

@@ -21,6 +21,7 @@ import { SettingTile } from '../../../components/setting-tile';
 import { useMatrixClient } from '../../../hooks/useMatrixClient';
 import { useRoom } from '../../../hooks/useRoom';
 import { StateEvent } from '../../../../types/matrix/room';
+import { sendStateEvent } from '../../../utils/room';
 import { AsyncStatus, useAsyncCallback } from '../../../hooks/useAsyncCallback';
 import { useStateEvent } from '../../../hooks/useStateEvent';
 import { stopPropagation } from '../../../utils/keyboard';
@@ -76,7 +77,7 @@ export function RoomHistoryVisibility({ permissions }: RoomHistoryVisibilityProp
         const content: RoomHistoryVisibilityEventContent = {
           history_visibility: visibility,
         };
-        await mx.sendStateEvent(room.roomId, StateEvent.RoomHistoryVisibility as any, content);
+        await sendStateEvent(mx, room.roomId, StateEvent.RoomHistoryVisibility, content);
       },
       [mx, room.roomId],
     ),