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/styles.css

@@ -162,6 +162,80 @@
   gap: 2px;
   flex-shrink: 0;
 }
+.miu-msg-time {
+  font-size: 11px;
+  color: var(--miu-muted);
+  flex-shrink: 0;
+  white-space: nowrap;
+}
+
+/* thread header + group/channel settings */
+.miu-thread-head {
+  flex: 0 0 auto;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+  padding: 10px 14px;
+  border-bottom: 1px solid var(--miu-border);
+}
+.miu-thread-title {
+  font-weight: 700;
+  font-size: 14px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.miu-thread-settings {
+  flex-shrink: 0;
+  border: none;
+  background: none;
+  color: var(--miu-muted);
+  cursor: pointer;
+  font-size: 16px;
+  line-height: 1;
+  padding: 4px;
+  border-radius: 8px;
+}
+.miu-thread-settings:hover {
+  background: var(--miu-panel-2);
+  color: var(--miu-text);
+}
+.miu-settings-list {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+  max-height: 240px;
+  overflow-y: auto;
+}
+.miu-settings-member {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 7px 10px;
+  border: 1px solid var(--miu-border);
+  border-radius: 10px;
+  background: var(--miu-panel);
+  color: var(--miu-text);
+  font-size: 13px;
+  text-align: left;
+}
+.miu-settings-member.is-add {
+  cursor: pointer;
+}
+.miu-settings-member.is-add:hover {
+  border-color: var(--miu-accent);
+}
+.miu-settings-name {
+  flex: 1 1 auto;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.miu-settings-plus {
+  color: var(--miu-accent);
+  font-weight: 700;
+}
 .miu-thread-link {
   align-self: flex-start;
   margin-top: 3px;