reply UX: show username + content preview instead of hash

- ComposeBox takes ReplyContext {id, username, content} instead of string
- Reply chip shows "^ benji message preview..." with truncation
- App passes full reply context from messagesById

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/colony/src/App.tsx

@@ -43,7 +43,7 @@ export default function App() {
   const [activeChannelId, setActiveChannelId] = useState<string | null>(null);
   const [messages, setMessages] = useState<Message[]>([]);
   const [loading, setLoading] = useState(false);
-  const [replyTo, setReplyTo] = useState<string | null>(null);
+  const [replyTo, setReplyTo] = useState<{ id: string; username: string; content: string } | null>(null);
   const [sheetOpen, setSheetOpen] = useState(false);
   const scrollRef = useRef<HTMLDivElement>(null);
   const prevMsgCountRef = useRef(0);
@@ -178,7 +178,12 @@ export default function App() {
                 key={msg.id}
                 message={msg}
                 replyTarget={msg.reply_to ? messagesById.get(msg.reply_to) : undefined}
-                onReply={setReplyTo}
+                onReply={(id) => {
+                  const target = messagesById.get(id);
+                  if (target) {
+                    setReplyTo({ id, username: target.user.display_name, content: target.content });
+                  }
+                }}
               />
             ))
           )}