feat(messaging-ui): mail attachment download + scrollable reader (0.1.1)

- Attachment chips in the mail reader are now clickable: new InboxAdapter
  downloadAttachment() resolves a short-lived URL, opened in a new tab.
- Mail reader scrolls again: convert the .miu-detail/.miu-mail height:100%
  chain to flex fill so a long thread scrolls within the pane instead of
  being clipped. MockInboxAdapter implements download. Bump to 0.1.1.

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

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

@@ -353,7 +353,15 @@
   white-space: nowrap;
 }
 .miu-mail-msg .miu-attach-chip {
-  margin-top: 6px;
+  margin: 8px 12px 12px;
+}
+button.miu-attach-dl {
+  cursor: pointer;
+  color: var(--miu-text);
+}
+button.miu-attach-dl:hover {
+  border-color: var(--miu-accent);
+  color: var(--miu-accent);
 }
 .miu-attach-pending {
   display: inline-flex;
@@ -763,7 +771,7 @@
 .miu-detail {
   display: flex;
   flex-direction: column;
-  height: 100%;
+  flex: 1;
   min-height: 0;
 }
 .miu-detail-actions {
@@ -790,7 +798,7 @@
 .miu-mail {
   display: flex;
   flex-direction: column;
-  height: 100%;
+  flex: 1;
   min-height: 0;
 }
 .miu-mail-head {