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/notify/notify_test.go

@@ -83,6 +83,18 @@ func TestYourTurnPayloadRoundTrips(t *testing.T) {
 	}
 }
 
+func TestNudgePayloadRoundTrips(t *testing.T) {
+	uid, gid, from := uuid.New(), uuid.New(), uuid.New()
+	in := notify.Nudge(uid, gid, from, "Ann")
+	if in.UserID != uid || in.Kind != notify.KindNudge || in.EventID == "" {
+		t.Fatalf("intent metadata wrong: %+v", in)
+	}
+	ev := fb.GetRootAsNudgeEvent(in.Payload, 0)
+	if string(ev.GameId()) != gid.String() || string(ev.FromUserId()) != from.String() || string(ev.SenderName()) != "Ann" {
+		t.Fatalf("nudge fields wrong: game=%q from=%q name=%q", ev.GameId(), ev.FromUserId(), ev.SenderName())
+	}
+}
+
 func TestGameOverPayloadRoundTrips(t *testing.T) {
 	uid, gid := uuid.New(), uuid.New()
 	summary := notify.GameSummary{ID: gid.String(), Status: "finished", MoveCount: 18, Seats: []notify.SeatStanding{{Seat: 0, Score: 120, IsWinner: true}}}