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/useSyncState.ts

@@ -3,7 +3,7 @@ import { useEffect } from 'react';
 
 export const useSyncState = (
   mx: MatrixClient | undefined,
-  onChange: ClientEventHandlerMap[ClientEvent.Sync]
+  onChange: ClientEventHandlerMap[ClientEvent.Sync],
 ): void => {
   useEffect(() => {
     mx?.on(ClientEvent.Sync, onChange);