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/game/service.go

@@ -1144,6 +1144,23 @@ func (svc *Service) Participants(ctx context.Context, gameID uuid.UUID) ([]uuid.
 	return seats, g.ToMove, g.Status, nil
 }
 
+// SeatName returns the display name shown for the account seated in the game — the seat's
+// captured snapshot, falling back to the account's current name (see seatDisplayName) — or ""
+// when the account holds no seat. It lets the social package name a nudge's sender by the same
+// per-game identity the rest of the game uses, without exposing the seats.
+func (svc *Service) SeatName(ctx context.Context, gameID, accountID uuid.UUID) (string, error) {
+	g, err := svc.store.GetGame(ctx, gameID)
+	if err != nil {
+		return "", err
+	}
+	for _, s := range g.Seats {
+		if s.AccountID == accountID {
+			return svc.seatDisplayName(ctx, s), nil
+		}
+	}
+	return "", nil
+}
+
 // SharedGame reports whether accounts a and b are seated together in any game
 // (active or finished). It backs the social package's "befriend an opponent"
 // request gate without exposing the games tables; a self-pair is never shared.