fix(web): unify mic/send button and restore scroll-down

- show one action button in composer: mic when empty, send when text exists

- add floating scroll-to-bottom button in message list

- exclude non-text/media messages from Chat Info links list to avoid duplicates

web/src/components/MessageList.tsx

@@ -67,6 +67,8 @@ export function MessageList() {
   const [undoTick, setUndoTick] = useState(0);
   const [reactionsByMessage, setReactionsByMessage] = useState<Record<number, MessageReaction[]>>({});
   const [mediaViewer, setMediaViewer] = useState<MediaViewerState>(null);
+  const [showScrollToBottom, setShowScrollToBottom] = useState(false);
+  const scrollContainerRef = useRef<HTMLDivElement | null>(null);
 
   const messages = useMemo(() => {
     if (!activeChatId) {
@@ -143,11 +145,28 @@ export function MessageList() {
     return () => window.clearTimeout(timer);
   }, [activeChatId, focusedMessageId, messages.length, setFocusedMessage]);
 
+  useEffect(() => {
+    const container = scrollContainerRef.current;
+    if (!container) {
+      return;
+    }
+    const distance = container.scrollHeight - container.scrollTop - container.clientHeight;
+    setShowScrollToBottom(distance > 180);
+  }, [messages.length, activeChatId]);
+
   if (!activeChatId) {
     return <div className="flex h-full items-center justify-center text-slate-300/80">Select a chat</div>;
   }
   const chatId = activeChatId;
 
+  function scrollToBottom() {
+    const container = scrollContainerRef.current;
+    if (!container) {
+      return;
+    }
+    container.scrollTo({ top: container.scrollHeight, behavior: "smooth" });
+  }
+
   async function ensureReactionsLoaded(messageId: number) {
     if (reactionsByMessage[messageId]) {
       return;
@@ -325,7 +344,15 @@ export function MessageList() {
         </div>
       ) : null}
 
-      <div className="tg-scrollbar flex-1 overflow-auto px-2 py-4 md:px-5">
+      <div
+        className="tg-scrollbar flex-1 overflow-auto px-2 py-4 md:px-5"
+        ref={scrollContainerRef}
+        onScroll={(event) => {
+          const target = event.currentTarget;
+          const distance = target.scrollHeight - target.scrollTop - target.clientHeight;
+          setShowScrollToBottom(distance > 180);
+        }}
+      >
         {hasMore ? (
           <div className="mb-3 flex justify-center">
             <button
@@ -466,6 +493,17 @@ export function MessageList() {
       </div>
 
       <div className="px-5 pb-2 text-xs text-slate-300/80">{(typingByChat[activeChatId] ?? []).length > 0 ? "typing..." : ""}</div>
+      {showScrollToBottom ? (
+        <div className="pointer-events-none absolute bottom-4 right-4 z-40">
+          <button
+            className="pointer-events-auto inline-flex h-10 w-10 items-center justify-center rounded-full border border-slate-600/80 bg-slate-900/90 text-lg text-slate-100 shadow-lg hover:bg-slate-800"
+            onClick={scrollToBottom}
+            type="button"
+          >
+            ↓
+          </button>
+        </div>
+      ) : null}
 
       {ctx
         ? createPortal(