feat(ui): hide GCG export in honest-AI games

A vs_ai game is throwaway practice, so its finished history header no longer
offers the 📤 GCG export (an empty slot keeps the comms icon pinned right).
Docs note the AI exclusion; UI_DESIGN also records that confirming a resign
reveals the full board (closes the history drawer, zooms out).

ui/src/game/Game.svelte

@@ -986,7 +986,13 @@
   {#if view}
     <div class="hhead">
       {#if gameOver}
-        <button class="hicon" onclick={exportGcg} aria-label={t('game.exportGcg')}>📤</button>
+        {#if view.game.vsAi}
+          <!-- GCG export is not offered for a practice AI game; an empty slot keeps the comms
+               icon pinned right (the header is space-between). -->
+          <span aria-hidden="true"></span>
+        {:else}
+          <button class="hicon" onclick={exportGcg} aria-label={t('game.exportGcg')}>📤</button>
+        {/if}
       {:else}
         <button class="hicon" onclick={() => (resignOpen = true)} disabled={waitingForOpponent} aria-label={t('game.dropGame')}>🏁</button>
       {/if}