feat: add Russian localization and independent STT languages

src/core/ports.ts

@@ -31,6 +31,8 @@ import type { UserSettings } from "./settings.ts";
 // ─── ChatStore — the session record's home (data/chats) ─────────────────────
 
 export interface ChatStore {
+	/** Persist automatic language context without altering activity ordering. */
+	saveLanguage?(id: string, language: "en" | "ru"): void;
 	/** Create a session record (persisted immediately). */
 	/** Create a session record; kind "practice" marks a practice session
 	 *  (absent = teach, the default). */