feat(telegram,game): single bot + per-user variant preferences

Collapse the two per-language Telegram bots into one unified bot and
replace language-based variant gating with explicit per-user variant
preferences.

- Telegram: one bot; drop service_language and the supported_languages
  set everywhere (DB, account, auth, FlatBuffers Session wire, gateway,
  connector proto). The single bot renders chat and out-of-app push in
  the recipient's preferred_language; remove the game-language push
  routing override (notify Intent.Language / push Event.language).
- Preferences: new accounts.variant_preferences (text[], DB default
  {erudit_ru}, CHECK non-empty + subset of the three variants). Gates
  the New Game picker, vs-AI and the friend invitation the player
  creates, enforced server-side (HTTP 400 otherwise); an invited friend
  may still accept any variant. Edited on the Settings screen; variants
  are Erudit-first everywhere.
- Admin: drop the per-bot language selectors (broadcast / send-to-user)
  and the feedback channel_lang column/field.
- Env/CI: collapse TELEGRAM_BOT_TOKEN_{EN,RU}, TELEGRAM_GAME_CHANNEL_ID_{EN,RU},
  VITE_TELEGRAM_LINK{,_EN,_RU} and VITE_TELEGRAM_GAME_CHANNEL_NAME_{EN,RU}
  to single unsuffixed names; drop GATEWAY_DEFAULT_SUPPORTED_LANGUAGES.
- Docs updated (ARCHITECTURE, FUNCTIONAL + _ru, platform/telegram, gateway,
  backend, ui, UI_DESIGN, PRERELEASE).

The migration squash is deferred to a follow-up PR.

backend/internal/feedback/service.go

@@ -112,14 +112,9 @@ func (svc *Service) Submit(ctx context.Context, accountID uuid.UUID, body string
 		attachmentName = "" // a name without bytes carries no attachment
 	}
 	ch := normalizeChannel(channel)
-	// Snapshot the languages at submit time (acc is already loaded for the guest check):
-	// the sender's interface language, and the connector bot language when the message
-	// came through an external connector (currently Telegram).
-	var channelLang string
-	if ch == "telegram" {
-		channelLang = acc.ServiceLanguage
-	}
-	_, err = svc.store.Insert(ctx, accountID, body, attachment, attachmentName, ch, acc.PreferredLanguage, channelLang, parseIP(senderIP))
+	// Snapshot the sender's interface language at submit time (acc is already loaded
+	// for the guest check) so the operator later sees the state as it was.
+	_, err = svc.store.Insert(ctx, accountID, body, attachment, attachmentName, ch, acc.PreferredLanguage, parseIP(senderIP))
 	return err
 }
 

backend/internal/feedback/store.go

@@ -34,11 +34,10 @@ func NewStore(db *sql.DB) *Store {
 
 // Insert stores one feedback message from accountID and returns its id. attachment
 // is the raw file bytes (nil for none); attachmentName, ip and a non-default
-// channel are stored as given. lang (the sender's interface language) and channelLang
-// (the connector bot language, empty for a non-connector channel) are snapshots taken
-// now, so the operator later sees the state at submit time. created_at defaults to
-// now() in the database.
-func (s *Store) Insert(ctx context.Context, accountID uuid.UUID, body string, attachment []byte, attachmentName, channel, lang, channelLang string, ip *string) (uuid.UUID, error) {
+// channel are stored as given. lang (the sender's interface language) is a snapshot
+// taken now, so the operator later sees the state at submit time. created_at defaults
+// to now() in the database.
+func (s *Store) Insert(ctx context.Context, accountID uuid.UUID, body string, attachment []byte, attachmentName, channel, lang string, ip *string) (uuid.UUID, error) {
 	id, err := uuid.NewV7()
 	if err != nil {
 		return uuid.Nil, fmt.Errorf("feedback: new message id: %w", err)
@@ -49,9 +48,9 @@ func (s *Store) Insert(ctx context.Context, accountID uuid.UUID, body string, at
 	}
 	if _, err := s.db.ExecContext(ctx,
 		`INSERT INTO backend.feedback_messages
-		   (message_id, account_id, body, attachment, attachment_name, channel, lang, channel_lang, sender_ip)
-		 VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)`,
-		id, accountID, body, att, nullStr(attachmentName), channel, nullStr(lang), nullStr(channelLang), ip); err != nil {
+		   (message_id, account_id, body, attachment, attachment_name, channel, lang, sender_ip)
+		 VALUES ($1, $2, $3, $4, $5, $6, $7, $8)`,
+		id, accountID, body, att, nullStr(attachmentName), channel, nullStr(lang), ip); err != nil {
 		return uuid.Nil, fmt.Errorf("feedback: insert: %w", err)
 	}
 	return id, nil
@@ -228,10 +227,8 @@ type AdminMessage struct {
 	Source     string
 	Body       string
 	Channel    string
-	// Lang is the sender's interface language and ChannelLang the connector bot language
-	// (en/ru, empty for a non-connector channel) — both snapshotted at submit time.
+	// Lang is the sender's interface language, snapshotted at submit time.
 	Lang           string
-	ChannelLang    string
 	SenderIP       string
 	HasAttachment  bool
 	AttachmentName string
@@ -346,7 +343,7 @@ func (s *Store) AdminGet(ctx context.Context, id uuid.UUID) (AdminMessage, error
 	var m AdminMessage
 	var repliedAt sql.NullTime
 	q := `SELECT m.message_id, m.account_id, a.display_name, ` + feedbackSource + ` AS source, m.body, m.channel,
-		COALESCE(m.lang, ''), COALESCE(m.channel_lang, ''),
+		COALESCE(m.lang, ''),
 		COALESCE(m.sender_ip, ''), (m.attachment IS NOT NULL), COALESCE(m.attachment_name, ''),
 		(m.read_at IS NOT NULL), (m.archived_at IS NOT NULL), (m.reply_body IS NOT NULL),
 		COALESCE(m.reply_body, ''), m.replied_at, m.created_at
@@ -355,7 +352,7 @@ func (s *Store) AdminGet(ctx context.Context, id uuid.UUID) (AdminMessage, error
 	WHERE m.message_id = $1`
 	err := s.db.QueryRowContext(ctx, q, id).Scan(
 		&m.ID, &m.AccountID, &m.SenderName, &m.Source, &m.Body, &m.Channel,
-		&m.Lang, &m.ChannelLang,
+		&m.Lang,
 		&m.SenderIP, &m.HasAttachment, &m.AttachmentName,
 		&m.Read, &m.Archived, &m.Replied, &m.ReplyBody, &repliedAt, &m.CreatedAt)
 	if errors.Is(err, sql.ErrNoRows) {