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.

pkg/fbs/scrabble.fbs

@@ -123,20 +123,11 @@ table EmailLoginRequest {
 }
 
 // Session is the minted credential returned by every auth operation.
-// supported_languages is the set of game languages (subset of {en, ru}, at least
-// one) the service the user signed in through offers; the UI gates the New Game
-// variant choice by it (en -> English; ru -> Russian + Эрудит). It is session-
-// scoped (not persisted) and added trailing — backward-compatible.
 table Session {
   token:string;
   user_id:string;
   is_guest:bool;
   display_name:string;
-  supported_languages:[string];
-  // service_language is the language tag (en/ru) of the Telegram bot the session was
-  // minted through; empty for a non-Telegram login. The UI uses it to build a share
-  // link that points at the same bot.
-  service_language:string;
 }
 
 // Ack is a simple success acknowledgement (e.g. an email-code request).
@@ -190,6 +181,9 @@ table Profile {
   away_end:string;
   notifications_in_app_only:bool = true;
   banner:BannerInfo;
+  // variant_preferences is the set of game variants the player allows themselves to be
+  // matched into (engine.Variant labels), Erudit-first; the New Game picker is gated by it.
+  variant_preferences:[string];
 }
 
 // BlockStatus reports the caller's current manual block. The UI fetches it after any operation
@@ -434,6 +428,7 @@ table UpdateProfileRequest {
   block_chat:bool;
   block_friend_requests:bool;
   notifications_in_app_only:bool = true;
+  variant_preferences:[string];
 }
 
 // --- account linking & merge (authenticated) ---

pkg/fbs/scrabblefb/Profile.go

@@ -162,8 +162,25 @@ func (rcv *Profile) Banner(obj *BannerInfo) *BannerInfo {
 	return nil
 }
 
+func (rcv *Profile) VariantPreferences(j int) []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(28))
+	if o != 0 {
+		a := rcv._tab.Vector(o)
+		return rcv._tab.ByteVector(a + flatbuffers.UOffsetT(j*4))
+	}
+	return nil
+}
+
+func (rcv *Profile) VariantPreferencesLength() int {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(28))
+	if o != 0 {
+		return rcv._tab.VectorLen(o)
+	}
+	return 0
+}
+
 func ProfileStart(builder *flatbuffers.Builder) {
-	builder.StartObject(12)
+	builder.StartObject(13)
 }
 func ProfileAddUserId(builder *flatbuffers.Builder, userId flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(userId), 0)
@@ -201,6 +218,12 @@ func ProfileAddNotificationsInAppOnly(builder *flatbuffers.Builder, notification
 func ProfileAddBanner(builder *flatbuffers.Builder, banner flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(11, flatbuffers.UOffsetT(banner), 0)
 }
+func ProfileAddVariantPreferences(builder *flatbuffers.Builder, variantPreferences flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(12, flatbuffers.UOffsetT(variantPreferences), 0)
+}
+func ProfileStartVariantPreferencesVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
+	return builder.StartVector(4, numElems, 4)
+}
 func ProfileEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }

pkg/fbs/scrabblefb/Session.go

@@ -77,33 +77,8 @@ func (rcv *Session) DisplayName() []byte {
 	return nil
 }
 
-func (rcv *Session) SupportedLanguages(j int) []byte {
-	o := flatbuffers.UOffsetT(rcv._tab.Offset(12))
-	if o != 0 {
-		a := rcv._tab.Vector(o)
-		return rcv._tab.ByteVector(a + flatbuffers.UOffsetT(j*4))
-	}
-	return nil
-}
-
-func (rcv *Session) SupportedLanguagesLength() int {
-	o := flatbuffers.UOffsetT(rcv._tab.Offset(12))
-	if o != 0 {
-		return rcv._tab.VectorLen(o)
-	}
-	return 0
-}
-
-func (rcv *Session) ServiceLanguage() []byte {
-	o := flatbuffers.UOffsetT(rcv._tab.Offset(14))
-	if o != 0 {
-		return rcv._tab.ByteVector(o + rcv._tab.Pos)
-	}
-	return nil
-}
-
 func SessionStart(builder *flatbuffers.Builder) {
-	builder.StartObject(6)
+	builder.StartObject(4)
 }
 func SessionAddToken(builder *flatbuffers.Builder, token flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(token), 0)
@@ -117,15 +92,6 @@ func SessionAddIsGuest(builder *flatbuffers.Builder, isGuest bool) {
 func SessionAddDisplayName(builder *flatbuffers.Builder, displayName flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(3, flatbuffers.UOffsetT(displayName), 0)
 }
-func SessionAddSupportedLanguages(builder *flatbuffers.Builder, supportedLanguages flatbuffers.UOffsetT) {
-	builder.PrependUOffsetTSlot(4, flatbuffers.UOffsetT(supportedLanguages), 0)
-}
-func SessionStartSupportedLanguagesVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
-	return builder.StartVector(4, numElems, 4)
-}
-func SessionAddServiceLanguage(builder *flatbuffers.Builder, serviceLanguage flatbuffers.UOffsetT) {
-	builder.PrependUOffsetTSlot(5, flatbuffers.UOffsetT(serviceLanguage), 0)
-}
 func SessionEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }

pkg/fbs/scrabblefb/UpdateProfileRequest.go

@@ -117,8 +117,25 @@ func (rcv *UpdateProfileRequest) MutateNotificationsInAppOnly(n bool) bool {
 	return rcv._tab.MutateBoolSlot(18, n)
 }
 
+func (rcv *UpdateProfileRequest) VariantPreferences(j int) []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(20))
+	if o != 0 {
+		a := rcv._tab.Vector(o)
+		return rcv._tab.ByteVector(a + flatbuffers.UOffsetT(j*4))
+	}
+	return nil
+}
+
+func (rcv *UpdateProfileRequest) VariantPreferencesLength() int {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(20))
+	if o != 0 {
+		return rcv._tab.VectorLen(o)
+	}
+	return 0
+}
+
 func UpdateProfileRequestStart(builder *flatbuffers.Builder) {
-	builder.StartObject(8)
+	builder.StartObject(9)
 }
 func UpdateProfileRequestAddDisplayName(builder *flatbuffers.Builder, displayName flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(displayName), 0)
@@ -144,6 +161,12 @@ func UpdateProfileRequestAddBlockFriendRequests(builder *flatbuffers.Builder, bl
 func UpdateProfileRequestAddNotificationsInAppOnly(builder *flatbuffers.Builder, notificationsInAppOnly bool) {
 	builder.PrependBoolSlot(7, notificationsInAppOnly, true)
 }
+func UpdateProfileRequestAddVariantPreferences(builder *flatbuffers.Builder, variantPreferences flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(8, flatbuffers.UOffsetT(variantPreferences), 0)
+}
+func UpdateProfileRequestStartVariantPreferencesVector(builder *flatbuffers.Builder, numElems int) flatbuffers.UOffsetT {
+	return builder.StartVector(4, numElems, 4)
+}
 func UpdateProfileRequestEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }