UI: gesture & history polish — pinch/swipe fix, wider back-swipe, nudge align, history overscroll

- Stop a two-finger pinch-out from also opening the history: the board wrapper arms its
  open/close pull only while a single pointer is down (a 2nd finger is a pinch, owned by Board).
- Widen the edge-swipe-back activation band to the left half of the viewport (was 20%).
- Align a chat nudge by sender like a bubble — your own to the right, the opponent's to the
  left (only the alignment changes).
- Kill the iOS rubber-band inside the history drawer (overscroll-behavior: none).

e2e: a two-finger pinch does not open the history; a back-swipe from the left half navigates back.

ui/src/game/Chat.svelte

@@ -42,7 +42,7 @@
     {/if}
     {#each messages as m (m.id)}
       {#if m.kind === 'nudge'}
-        <div class="note">{t('chat.nudge')}</div>
+        <div class="note" class:mine={m.senderId === myId}>{t('chat.nudge')}</div>
       {:else}
         <div class="msg" class:mine={m.senderId === myId}>{m.body}</div>
       {/if}
@@ -104,11 +104,16 @@
     color: var(--accent-text);
   }
   .note {
-    align-self: center;
+    /* A nudge aligns by sender, like a chat bubble: the opponent's hurry-up reads from the
+       left, your own from the right — only the alignment changes, the muted italic stays. */
+    align-self: flex-start;
     font-size: 0.82rem;
     color: var(--text-muted);
     font-style: italic;
   }
+  .note.mine {
+    align-self: flex-end;
+  }
   .input {
     display: flex;
     gap: 6px;