chore: upgrade i18next 26, prettier 3, fontsource-variable, domhandler 6, lint-staged 17

- i18next 23->26 + react-i18next 15->17
- prettier 2->3, reformat all files
- replace @fontsource/inter with @fontsource-variable/inter 5, update import path
- domhandler 5->6 (aligns with transitive deps)
- lint-staged 16->17

src/app/components/leave-room-prompt/LeaveRoomPrompt.tsx

@@ -32,7 +32,7 @@ export function LeaveRoomPrompt({ roomId, onDone, onCancel }: LeaveRoomPromptPro
   const [leaveState, leaveRoom] = useAsyncCallback<undefined, MatrixError, []>(
     useCallback(async () => {
       mx.leave(roomId);
-    }, [mx, roomId])
+    }, [mx, roomId]),
   );
 
   const handleLeave = () => {