fix(timeline): read-position membership listener actually fires

RoomMemberEvent.Membership is emitted on RoomMember/MatrixClient, never
on Room, so the (room as any).on() handler was dead. Subscribe on the
client filtered by roomId; drop the cast.

Fixes #61

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/hooks/useRoomReadPositions.ts

@@ -1,4 +1,4 @@
-import { Room, RoomEvent, RoomMemberEvent, MatrixEvent } from 'matrix-js-sdk';
+import { Room, RoomEvent, RoomMember, RoomMemberEvent, MatrixEvent } from 'matrix-js-sdk';
 import { useEffect, useState } from 'react';
 import { useMatrixClient } from './useMatrixClient';
 import { reactionOrEditEvent } from '../utils/room';
@@ -52,15 +52,21 @@ export function useRoomReadPositions(room: Room): Map<string, string[]> {
         debounceTimer = null;
       }, 150);
     };
-    const onMembership = (): void => setPositions(computePositions(room, myUserId));
+    // RoomMemberEvent.Membership is emitted on the RoomMember (and re-emitted on the
+    // MatrixClient), never on Room — listening on `room` never fired. Subscribe on
+    // the client and filter to this room (Gitea #61).
+    const onMembership = (_ev: MatrixEvent, member: RoomMember): void => {
+      if (member.roomId !== room.roomId) return;
+      setPositions(computePositions(room, myUserId));
+    };
     room.on(RoomEvent.Receipt, onReceipt);
-    (room as any).on(RoomMemberEvent.Membership, onMembership);
+    mx.on(RoomMemberEvent.Membership, onMembership);
     return () => {
       if (debounceTimer !== null) clearTimeout(debounceTimer);
       room.removeListener(RoomEvent.Receipt, onReceipt);
-      (room as any).removeListener(RoomMemberEvent.Membership, onMembership);
+      mx.removeListener(RoomMemberEvent.Membership, onMembership);
     };
-  }, [room, myUserId]);
+  }, [room, myUserId, mx]);
 
   return positions;
 }