feat(nudge): name the sender; blink lobby cards; re-animate toasts

The "waiting for your move" popup was the nudge (chat.nudge), shown without a
sender name. Resolve the nudger's per-game seat name server-side and carry it on
a new NudgeEvent.sender_name field, so:

- the in-app toast reads "<opponent>: Waiting for your move 🤭" (chat.nudgeBy);
- the out-of-app Telegram push names the sender too (render nudgeBy);

falling back to the plain phrase when the name is absent (RU mirrored). The
your_turn toast already named the opponent and is unchanged.

Lobby: when a card transitions into "your turn" or "finished" while the lobby is
open, its status emoji blinks twice (two 1s fades); the opponent's-turn change
stays in place. Blink state is keyed by game id (SvelteSet + per-id nonce/timer)
so overlapping events animate in isolation; suppressed under reduce-motion.

Toast: a per-message seq re-keys Toast.svelte, so the freshest toast cancels the
previous one and replays its entrance, uniformly on every screen.

Tests: notify.Nudge round-trip + render named/fallback (Go), game.Service.SeatName
(integration), codec/i18n/gamePhase/shouldBlink (UI). Docs (FUNCTIONAL +_ru,
UI_DESIGN) + PLAN TODO-7 (deferred FLIP card-relocation animation) updated.

backend/internal/inttest/social_test.go

@@ -382,6 +382,33 @@ func TestNudgeRulesAndRateLimit(t *testing.T) {
 	}
 }
 
+// TestSeatNameResolvesDisplayName checks game.Service.SeatName surfaces a seated account's
+// display name — the identity social.Nudge voices the nudge with — and returns "" for an account
+// that holds no seat (the render then falls back to the plain phrase).
+func TestSeatNameResolvesDisplayName(t *testing.T) {
+	ctx := context.Background()
+	gsvc := newGameService()
+	// ProvisionRobot is the one provisioning path that stamps a known display name (a plain
+	// provisioned account has none), so the seat resolves to a name we can assert.
+	named, err := account.NewStore(testDB).ProvisionRobot(ctx, "tg-"+uuid.NewString(), "Ann")
+	if err != nil {
+		t.Fatalf("provision named account: %v", err)
+	}
+	g, err := gsvc.Create(ctx, game.CreateParams{
+		Variant: engine.VariantEnglish, Seats: []uuid.UUID{provisionAccount(t), named.ID},
+		TurnTimeout: 24 * time.Hour, Seed: openingSeed(t),
+	})
+	if err != nil {
+		t.Fatalf("create: %v", err)
+	}
+	if got, err := gsvc.SeatName(ctx, g.ID, named.ID); err != nil || got != "Ann" {
+		t.Errorf("seated SeatName = (%q, %v), want (\"Ann\", nil)", got, err)
+	}
+	if got, err := gsvc.SeatName(ctx, g.ID, provisionAccount(t)); err != nil || got != "" {
+		t.Errorf("non-seated SeatName = (%q, %v), want (\"\", nil)", got, err)
+	}
+}
+
 // TestNudgeCooldownResetsOnAction checks the nudge cooldown clears once the player has
 // acted (moved or chatted) since their last nudge, even within the hour.
 func TestNudgeCooldownResetsOnAction(t *testing.T) {