feat(messaging-ui): message timestamps + group/channel settings panel (0.1.5)

- Every message now shows a Slack-style time (clock today, then 'Yesterday',
  weekday, else a date; full timestamp on hover).
- New ConversationSettings panel for groups AND channels (public + private):
  rename, member list, add people (from the directory), remove, and leave.
  Opened from a new thread header gear; DMs show no gear. Adapter gains
  addMember/removeMember/renameConversation (optional, OPA still gates writes).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-messaging-ui/src/components/message-item.tsx

@@ -8,6 +8,20 @@ const REACTION_EMOJIS = ['👍', '❤️', '😂', '🎉', '👀'];
 
 const isImage = (mime: string): boolean => mime.startsWith('image/');
 
+/** Slack-style message time: today shows the clock, then "Yesterday", weekday, else a date. */
+function messageTime(iso: string): string {
+  const d = new Date(iso);
+  if (Number.isNaN(+d)) return '';
+  const now = new Date();
+  const time = d.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' });
+  if (d.toDateString() === now.toDateString()) return time;
+  const yesterday = new Date(now);
+  yesterday.setDate(now.getDate() - 1);
+  if (d.toDateString() === yesterday.toDateString()) return `Yesterday ${time}`;
+  if (now.getTime() - d.getTime() < 7 * 86400000) return `${d.toLocaleDateString([], { weekday: 'short' })} ${time}`;
+  return `${d.toLocaleDateString([], { month: 'short', day: 'numeric' })} ${time}`;
+}
+
 function AttachmentView({ att }: { att: Attachment }) {
   if (isImage(att.mime)) {
     return (
@@ -54,6 +68,9 @@ export function MessageItem({
           {m.text ? highlightMentions(m.text, memberNames) : null}
           {m.attachment ? <AttachmentView att={m.attachment} /> : null}
         </div>
+        <time className="miu-msg-time" dateTime={m.at} title={Number.isNaN(+new Date(m.at)) ? '' : new Date(m.at).toLocaleString()}>
+          {messageTime(m.at)}
+        </time>
         <div className="miu-msg-actions">
           {canReact ? (
             <div className="miu-react-wrap">