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/useRoomReadPositions.ts

@@ -8,7 +8,7 @@ import { reactionOrEditEvent } from '../utils/room';
 function nearestRenderableId(
   liveEvents: MatrixEvent[],
   eventIndex: Map<string, number>,
-  evtId: string
+  evtId: string,
 ): string | null {
   const idx = eventIndex.get(evtId) ?? -1;
   if (idx === -1) return null;