feat(chat): align activity timing UI with hover-only end timestamps (#557)

* feat(chat): add shared activity timestamp formatter

* feat(chat): pass assistant created timestamp to message body

* feat(chat): render footer timestamp beside elapsed time

* feat(chat): pass timing metadata in reasoning text blocks

* feat(chat): propagate justification timing to timeline block

* feat(chat): show thinking duration with hover end time

* feat(chat): reveal tool end time on activity hover

packages/ui/src/components/chat/message/parts/AssistantTextPart.tsx

@@ -61,6 +61,7 @@ const AssistantTextPart: React.FC<AssistantTextPartProps> = ({
                 variant="justification"
                 onContentChange={onContentChange}
                 blockId={part.id || `${messageId}-reasoning-text`}
+                time={time}
             />
         );
     }