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.

pkg/fbs/scrabblefb/NudgeEvent.go

@@ -57,8 +57,16 @@ func (rcv *NudgeEvent) FromUserId() []byte {
 	return nil
 }
 
+func (rcv *NudgeEvent) SenderName() []byte {
+	o := flatbuffers.UOffsetT(rcv._tab.Offset(8))
+	if o != 0 {
+		return rcv._tab.ByteVector(o + rcv._tab.Pos)
+	}
+	return nil
+}
+
 func NudgeEventStart(builder *flatbuffers.Builder) {
-	builder.StartObject(2)
+	builder.StartObject(3)
 }
 func NudgeEventAddGameId(builder *flatbuffers.Builder, gameId flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(0, flatbuffers.UOffsetT(gameId), 0)
@@ -66,6 +74,9 @@ func NudgeEventAddGameId(builder *flatbuffers.Builder, gameId flatbuffers.UOffse
 func NudgeEventAddFromUserId(builder *flatbuffers.Builder, fromUserId flatbuffers.UOffsetT) {
 	builder.PrependUOffsetTSlot(1, flatbuffers.UOffsetT(fromUserId), 0)
 }
+func NudgeEventAddSenderName(builder *flatbuffers.Builder, senderName flatbuffers.UOffsetT) {
+	builder.PrependUOffsetTSlot(2, flatbuffers.UOffsetT(senderName), 0)
+}
 func NudgeEventEnd(builder *flatbuffers.Builder) flatbuffers.UOffsetT {
 	return builder.EndObject()
 }