floating action pill + auto-scroll on send + channel ordering

- Actions: floating pill top-right with ↩ and × (slides in on hover)
- No more ugly REPLY DEL text — minimal symbols, backdrop shadow
- Delete button only shows for own messages
- Auto-scroll to bottom after sending a message
- Channels sorted by last opened in sidebar

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

ui/colony/src/App.tsx

@@ -214,7 +214,17 @@ export default function App() {
             channelId={activeChannelId}
             replyTo={replyTo}
             onClearReply={() => setReplyTo(null)}
-            onMessageSent={loadMessages}
+            onMessageSent={() => {
+              loadMessages();
+              // Force scroll to bottom after sending
+              setTimeout(() => {
+                if (scrollRef.current) {
+                  const el = scrollRef.current as unknown as HTMLElement;
+                  const viewport = el.querySelector('[data-slot="scroll-area-viewport"]') || el;
+                  viewport.scrollTop = viewport.scrollHeight;
+                }
+              }, 100);
+            }}
           />
         )}
       </div>