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/hooks/useStateEventCallback.ts

@@ -4,7 +4,7 @@ import { useEffect } from 'react';
 export type StateEventCallback = (
   event: MatrixEvent,
   state: RoomState,
-  lastStateEvent: MatrixEvent | null
+  lastStateEvent: MatrixEvent | null,
 ) => void;
 
 export const useStateEventCallback = (mx: MatrixClient, onStateEvent: StateEventCallback) => {