feat(messaging-ui): attachments in inbox mail — reply + compose upload

InboxAdapter gains uploadAttachment + attachment params on mailReply/
composeInternal/composeExternal. MailReader reply and ComposeModal grow an
attach affordance (paperclip + pending chips); mail history renders sent
attachments. MockInboxAdapter implements upload. 67 tests green.

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

packages/iios-messaging-ui/src/styles.css

@@ -335,6 +335,46 @@
   padding: 0;
   line-height: 1;
 }
+
+/* inbox mail attachments */
+.miu-attach-chip {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+  padding: 4px 10px;
+  border-radius: 999px;
+  border: 1px solid var(--miu-border);
+  background: var(--miu-panel-2);
+  color: var(--miu-text);
+  font-size: 12.5px;
+  max-width: 100%;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.miu-mail-msg .miu-attach-chip {
+  margin-top: 6px;
+}
+.miu-attach-pending {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+}
+.miu-attach-x {
+  border: none;
+  background: none;
+  color: var(--miu-muted);
+  cursor: pointer;
+  padding: 0 2px;
+  line-height: 1;
+  font-size: 12px;
+}
+.miu-attach-list {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 8px;
+}
 .miu-suggest {
   position: absolute;
   left: 12px;