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.

ui/src/components/Toast.svelte

@@ -6,15 +6,19 @@
 </script>
 
 {#if app.toast}
-  <div
-    class="toast {app.toast.kind}"
-    role="status"
-    aria-live="polite"
-    in:fly={{ y: 32, duration: dur }}
-    out:fade={{ duration: dur }}
-  >
-    {app.toast.text}
-  </div>
+  <!-- Re-key on the toast's seq so a fresh message tears the old node down (out:fade) and replays
+       the entrance (in:fly): the newest toast cancels the previous one and starts its own cycle. -->
+  {#key app.toast.seq}
+    <div
+      class="toast {app.toast.kind}"
+      role="status"
+      aria-live="polite"
+      in:fly={{ y: 32, duration: dur }}
+      out:fade={{ duration: dur }}
+    >
+      {app.toast.text}
+    </div>
+  {/key}
 {/if}
 
 <style>