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.

platform/telegram/internal/config/config_test.go

@@ -6,33 +6,38 @@ import (
 	pkgtel "scrabble/pkg/telemetry"
 )
 
-// setRequired sets the required connector variables (one bot + the Mini App URL)
-// so Load reaches the telemetry checks.
+// setRequired sets the required connector variables (the bot token + the Mini App
+// URL) so Load reaches the telemetry checks.
 func setRequired(t *testing.T) {
 	t.Helper()
-	t.Setenv("TELEGRAM_BOT_TOKEN_EN", "test-token")
+	t.Setenv("TELEGRAM_BOT_TOKEN", "test-token")
 	t.Setenv("TELEGRAM_MINIAPP_URL", "https://example.org/app")
 }
 
-// TestLoadBots verifies the per-language bot parsing: a present token enables a
-// language, its channel id is optional, and the result is keyed by language.
-func TestLoadBots(t *testing.T) {
+// TestLoadBot verifies the bot parsing: the token is read and the game channel id is
+// parsed when present.
+func TestLoadBot(t *testing.T) {
 	t.Setenv("TELEGRAM_MINIAPP_URL", "https://example.org/app")
-	t.Setenv("TELEGRAM_BOT_TOKEN_EN", "en-token")
-	t.Setenv("TELEGRAM_GAME_CHANNEL_ID_EN", "-100111")
-	t.Setenv("TELEGRAM_BOT_TOKEN_RU", "ru-token")
+	t.Setenv("TELEGRAM_BOT_TOKEN", "bot-token")
+	t.Setenv("TELEGRAM_GAME_CHANNEL_ID", "-100111")
 	c, err := Load()
 	if err != nil {
 		t.Fatalf("Load: %v", err)
 	}
-	if len(c.Bots) != 2 {
-		t.Fatalf("Bots = %d, want 2", len(c.Bots))
+	if c.Token != "bot-token" || c.GameChannelID != -100111 {
+		t.Errorf("config = token %q / channel %d, want bot-token / -100111", c.Token, c.GameChannelID)
 	}
-	if c.Bots["en"].Token != "en-token" || c.Bots["en"].GameChannelID != -100111 {
-		t.Errorf("en bot = %+v", c.Bots["en"])
+}
+
+// TestLoadOptionalChannel verifies the game channel id defaults to 0 when unset.
+func TestLoadOptionalChannel(t *testing.T) {
+	setRequired(t)
+	c, err := Load()
+	if err != nil {
+		t.Fatalf("Load: %v", err)
 	}
-	if c.Bots["ru"].Token != "ru-token" || c.Bots["ru"].GameChannelID != 0 {
-		t.Errorf("ru bot = %+v, want token ru-token / channel 0", c.Bots["ru"])
+	if c.GameChannelID != 0 {
+		t.Errorf("GameChannelID = %d, want 0", c.GameChannelID)
 	}
 }