click-to-select for multi-reply + /new command + layout fix

- Click any message to select it for reply (click again to deselect)
- Multiple messages can be selected — compose shows all
- Selected messages get orange left border + tinted bg
- Floating pill shows ✓ when selected
- /new <name> slash command creates channels from compose box
- Proper multi-reply context in compose with count

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<{ id: string; username: string; content: string } | null>(null);
+  const [selectedMessages, setSelectedMessages] = useState<{ id: string; username: string; content: string }[]>([]);
   const [sheetOpen, setSheetOpen] = useState(false);
   const [showScrollDown, setShowScrollDown] = useState(false);
   const scrollRef = useRef<HTMLDivElement>(null);
@@ -93,7 +93,7 @@ export default function App() {
 
   useEffect(() => {
     setMessages([]);
-    setReplyTo(null);
+    setSelectedMessages([]);
     prevMsgCountRef.current = 0;
     loadMessages();
   }, [activeChannelId, loadMessages]);
@@ -212,11 +212,15 @@ export default function App() {
                 message={msg}
                 replyTarget={msg.reply_to ? messagesById.get(msg.reply_to) : undefined}
                 currentUsername={getCurrentUsername()}
-                onReply={(id) => {
-                  const target = messagesById.get(id);
-                  if (target) {
-                    setReplyTo({ id, username: target.user.display_name, content: target.content });
-                  }
+                selected={selectedMessages.some((s) => s.id === msg.id)}
+                onSelect={(id) => {
+                  setSelectedMessages((prev) => {
+                    const exists = prev.find((s) => s.id === id);
+                    if (exists) return prev.filter((s) => s.id !== id);
+                    const target = messagesById.get(id);
+                    if (!target) return prev;
+                    return [...prev, { id, username: target.user.display_name, content: target.content }];
+                  });
                 }}
                 onDelete={async (chId, msgId) => {
                   try {
@@ -248,9 +252,11 @@ export default function App() {
           <ComposeBox
             key={activeChannelId}
             channelId={activeChannelId}
-            replyTo={replyTo}
-            onClearReply={() => setReplyTo(null)}
+            replyTo={selectedMessages.length > 0 ? selectedMessages[0] : null}
+            selectedMessages={selectedMessages}
+            onClearReply={() => setSelectedMessages([])}
             onMessageSent={() => {
+              setSelectedMessages([]);
               loadMessages();
               setTimeout(() => scrollToBottom(), 100);
             }}