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/postgres/jet/backend/model/accounts.go

@@ -9,6 +9,7 @@ package model
 
 import (
 	"github.com/google/uuid"
+	"github.com/lib/pq"
 	"time"
 )
 
@@ -29,6 +30,6 @@ type Accounts struct {
 	PaidAccount            bool
 	MergedInto             *uuid.UUID
 	MergedAt               *time.Time
-	ServiceLanguage        *string
 	FlaggedHighRateAt      *time.Time
+	VariantPreferences     pq.StringArray
 }

backend/internal/postgres/jet/backend/model/feedback_messages.go

@@ -20,12 +20,11 @@ type FeedbackMessages struct {
 	AttachmentName *string
 	SenderIP       *string
 	Channel        string
-	Lang           *string
-	ChannelLang    *string
 	ReadAt         *time.Time
 	ArchivedAt     *time.Time
 	ReplyBody      *string
 	RepliedAt      *time.Time
 	ReplyReadAt    *time.Time
 	CreatedAt      time.Time
+	Lang           *string
 }

backend/internal/postgres/jet/backend/table/accounts.go

@@ -33,8 +33,8 @@ type accountsTable struct {
 	PaidAccount            postgres.ColumnBool
 	MergedInto             postgres.ColumnString
 	MergedAt               postgres.ColumnTimestampz
-	ServiceLanguage        postgres.ColumnString
 	FlaggedHighRateAt      postgres.ColumnTimestampz
+	VariantPreferences     postgres.ColumnStringArray
 
 	AllColumns     postgres.ColumnList
 	MutableColumns postgres.ColumnList
@@ -92,11 +92,11 @@ func newAccountsTableImpl(schemaName, tableName, alias string) accountsTable {
 		PaidAccountColumn            = postgres.BoolColumn("paid_account")
 		MergedIntoColumn             = postgres.StringColumn("merged_into")
 		MergedAtColumn               = postgres.TimestampzColumn("merged_at")
-		ServiceLanguageColumn        = postgres.StringColumn("service_language")
 		FlaggedHighRateAtColumn      = postgres.TimestampzColumn("flagged_high_rate_at")
-		allColumns                   = postgres.ColumnList{AccountIDColumn, DisplayNameColumn, PreferredLanguageColumn, TimeZoneColumn, BlockChatColumn, BlockFriendRequestsColumn, CreatedAtColumn, UpdatedAtColumn, AwayStartColumn, AwayEndColumn, HintBalanceColumn, IsGuestColumn, NotificationsInAppOnlyColumn, PaidAccountColumn, MergedIntoColumn, MergedAtColumn, ServiceLanguageColumn, FlaggedHighRateAtColumn}
-		mutableColumns               = postgres.ColumnList{DisplayNameColumn, PreferredLanguageColumn, TimeZoneColumn, BlockChatColumn, BlockFriendRequestsColumn, CreatedAtColumn, UpdatedAtColumn, AwayStartColumn, AwayEndColumn, HintBalanceColumn, IsGuestColumn, NotificationsInAppOnlyColumn, PaidAccountColumn, MergedIntoColumn, MergedAtColumn, ServiceLanguageColumn, FlaggedHighRateAtColumn}
-		defaultColumns               = postgres.ColumnList{DisplayNameColumn, PreferredLanguageColumn, TimeZoneColumn, BlockChatColumn, BlockFriendRequestsColumn, CreatedAtColumn, UpdatedAtColumn, AwayStartColumn, AwayEndColumn, HintBalanceColumn, IsGuestColumn, NotificationsInAppOnlyColumn, PaidAccountColumn}
+		VariantPreferencesColumn     = postgres.StringArrayColumn("variant_preferences")
+		allColumns                   = postgres.ColumnList{AccountIDColumn, DisplayNameColumn, PreferredLanguageColumn, TimeZoneColumn, BlockChatColumn, BlockFriendRequestsColumn, CreatedAtColumn, UpdatedAtColumn, AwayStartColumn, AwayEndColumn, HintBalanceColumn, IsGuestColumn, NotificationsInAppOnlyColumn, PaidAccountColumn, MergedIntoColumn, MergedAtColumn, FlaggedHighRateAtColumn, VariantPreferencesColumn}
+		mutableColumns               = postgres.ColumnList{DisplayNameColumn, PreferredLanguageColumn, TimeZoneColumn, BlockChatColumn, BlockFriendRequestsColumn, CreatedAtColumn, UpdatedAtColumn, AwayStartColumn, AwayEndColumn, HintBalanceColumn, IsGuestColumn, NotificationsInAppOnlyColumn, PaidAccountColumn, MergedIntoColumn, MergedAtColumn, FlaggedHighRateAtColumn, VariantPreferencesColumn}
+		defaultColumns               = postgres.ColumnList{DisplayNameColumn, PreferredLanguageColumn, TimeZoneColumn, BlockChatColumn, BlockFriendRequestsColumn, CreatedAtColumn, UpdatedAtColumn, AwayStartColumn, AwayEndColumn, HintBalanceColumn, IsGuestColumn, NotificationsInAppOnlyColumn, PaidAccountColumn, VariantPreferencesColumn}
 	)
 
 	return accountsTable{
@@ -119,8 +119,8 @@ func newAccountsTableImpl(schemaName, tableName, alias string) accountsTable {
 		PaidAccount:            PaidAccountColumn,
 		MergedInto:             MergedIntoColumn,
 		MergedAt:               MergedAtColumn,
-		ServiceLanguage:        ServiceLanguageColumn,
 		FlaggedHighRateAt:      FlaggedHighRateAtColumn,
+		VariantPreferences:     VariantPreferencesColumn,
 
 		AllColumns:     allColumns,
 		MutableColumns: mutableColumns,

backend/internal/postgres/jet/backend/table/feedback_messages.go

@@ -24,14 +24,13 @@ type feedbackMessagesTable struct {
 	AttachmentName postgres.ColumnString
 	SenderIP       postgres.ColumnString
 	Channel        postgres.ColumnString
-	Lang           postgres.ColumnString
-	ChannelLang    postgres.ColumnString
 	ReadAt         postgres.ColumnTimestampz
 	ArchivedAt     postgres.ColumnTimestampz
 	ReplyBody      postgres.ColumnString
 	RepliedAt      postgres.ColumnTimestampz
 	ReplyReadAt    postgres.ColumnTimestampz
 	CreatedAt      postgres.ColumnTimestampz
+	Lang           postgres.ColumnString
 
 	AllColumns     postgres.ColumnList
 	MutableColumns postgres.ColumnList
@@ -80,16 +79,15 @@ func newFeedbackMessagesTableImpl(schemaName, tableName, alias string) feedbackM
 		AttachmentNameColumn = postgres.StringColumn("attachment_name")
 		SenderIPColumn       = postgres.StringColumn("sender_ip")
 		ChannelColumn        = postgres.StringColumn("channel")
-		LangColumn           = postgres.StringColumn("lang")
-		ChannelLangColumn    = postgres.StringColumn("channel_lang")
 		ReadAtColumn         = postgres.TimestampzColumn("read_at")
 		ArchivedAtColumn     = postgres.TimestampzColumn("archived_at")
 		ReplyBodyColumn      = postgres.StringColumn("reply_body")
 		RepliedAtColumn      = postgres.TimestampzColumn("replied_at")
 		ReplyReadAtColumn    = postgres.TimestampzColumn("reply_read_at")
 		CreatedAtColumn      = postgres.TimestampzColumn("created_at")
-		allColumns           = postgres.ColumnList{MessageIDColumn, AccountIDColumn, BodyColumn, AttachmentColumn, AttachmentNameColumn, SenderIPColumn, ChannelColumn, LangColumn, ChannelLangColumn, ReadAtColumn, ArchivedAtColumn, ReplyBodyColumn, RepliedAtColumn, ReplyReadAtColumn, CreatedAtColumn}
-		mutableColumns       = postgres.ColumnList{AccountIDColumn, BodyColumn, AttachmentColumn, AttachmentNameColumn, SenderIPColumn, ChannelColumn, LangColumn, ChannelLangColumn, ReadAtColumn, ArchivedAtColumn, ReplyBodyColumn, RepliedAtColumn, ReplyReadAtColumn, CreatedAtColumn}
+		LangColumn           = postgres.StringColumn("lang")
+		allColumns           = postgres.ColumnList{MessageIDColumn, AccountIDColumn, BodyColumn, AttachmentColumn, AttachmentNameColumn, SenderIPColumn, ChannelColumn, ReadAtColumn, ArchivedAtColumn, ReplyBodyColumn, RepliedAtColumn, ReplyReadAtColumn, CreatedAtColumn, LangColumn}
+		mutableColumns       = postgres.ColumnList{AccountIDColumn, BodyColumn, AttachmentColumn, AttachmentNameColumn, SenderIPColumn, ChannelColumn, ReadAtColumn, ArchivedAtColumn, ReplyBodyColumn, RepliedAtColumn, ReplyReadAtColumn, CreatedAtColumn, LangColumn}
 		defaultColumns       = postgres.ColumnList{CreatedAtColumn}
 	)
 
@@ -104,14 +102,13 @@ func newFeedbackMessagesTableImpl(schemaName, tableName, alias string) feedbackM
 		AttachmentName: AttachmentNameColumn,
 		SenderIP:       SenderIPColumn,
 		Channel:        ChannelColumn,
-		Lang:           LangColumn,
-		ChannelLang:    ChannelLangColumn,
 		ReadAt:         ReadAtColumn,
 		ArchivedAt:     ArchivedAtColumn,
 		ReplyBody:      ReplyBodyColumn,
 		RepliedAt:      RepliedAtColumn,
 		ReplyReadAt:    ReplyReadAtColumn,
 		CreatedAt:      CreatedAtColumn,
+		Lang:           LangColumn,
 
 		AllColumns:     allColumns,
 		MutableColumns: mutableColumns,