Phone: keyboard no longer leaves the page shifted

Mobile browsers scroll the whole page up to show the focused input and do not
always scroll it back when the keyboard closes; the app never scrolls the page
itself, so the top bar (menu) stayed out of reach.

- Viewport interactive-widget=resizes-content: on Android the keyboard shrinks
  the page instead of shifting it.
- Elsewhere (iOS Safari) the page offset is undone when the visual viewport
  grows again or the input loses focus.
- The chat keeps following the latest message when its pane shrinks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/components/ChatView.tsx

@@ -202,6 +202,17 @@ export function ChatView({ sessionId, onMenu, onClosePane }: { sessionId: string
     const el = scrollRef.current;
     if (el && stick.current) el.scrollTop = el.scrollHeight;
   });
+  // … also when the pane gets smaller (on-screen keyboard opens) without a render.
+  const hasSession = !!session;
+  useEffect(() => {
+    const el = scrollRef.current;
+    if (!el || typeof ResizeObserver === "undefined") return;
+    const ro = new ResizeObserver(() => {
+      if (stick.current) el.scrollTop = el.scrollHeight;
+    });
+    ro.observe(el);
+    return () => ro.disconnect();
+  }, [hasSession, sessionId]);
 
   if (loadError) return <div className="empty">{loadError}</div>;
   if (!session) return <div className="empty">{t("common.loading")}</div>;