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/events.go

@@ -96,14 +96,18 @@ func ChatMessage(userID, gameID, senderID uuid.UUID, id, kind, body string, crea
 	return Intent{UserID: userID, Kind: KindChatMessage, Payload: b.FinishedBytes(), EventID: eventID()}
 }
 
-// Nudge tells userID that fromUserID nudged them in game gameID.
-func Nudge(userID, gameID, fromUserID uuid.UUID) Intent {
+// Nudge tells userID that fromUserID nudged them in game gameID. senderName is fromUserID's
+// seat display name, used to voice the toast and the out-of-app push ("<name>: …"); an empty
+// name leaves the render to fall back to the plain phrase.
+func Nudge(userID, gameID, fromUserID uuid.UUID, senderName string) Intent {
 	b := flatbuffers.NewBuilder(64)
 	gid := b.CreateString(gameID.String())
 	from := b.CreateString(fromUserID.String())
+	name := b.CreateString(senderName)
 	fb.NudgeEventStart(b)
 	fb.NudgeEventAddGameId(b, gid)
 	fb.NudgeEventAddFromUserId(b, from)
+	fb.NudgeEventAddSenderName(b, name)
 	b.Finish(fb.NudgeEventEnd(b))
 	return Intent{UserID: userID, Kind: KindNudge, Payload: b.FinishedBytes(), EventID: eventID()}
 }