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/inbox/inbox.tsx

@@ -117,7 +117,7 @@ function Detail({ item, onTransition }: { item: InboxItem; onTransition: (state:
 
 /** Read a mail thread (HTML in a sandboxed iframe) + reply. */
 export function MailReader({ threadId, subject }: { threadId: string; subject: string }) {
-  const { messages, loading, error, reply, canAttach, upload } = useMailThread(threadId);
+  const { messages, loading, error, reply, canAttach, upload, canDownload, download } = useMailThread(threadId);
   const [draft, setDraft] = useState('');
   const [sending, setSending] = useState(false);
   const [pending, setPending] = useState<MailAttachment | null>(null);
@@ -125,6 +125,15 @@ export function MailReader({ threadId, subject }: { threadId: string; subject: s
   const [attachErr, setAttachErr] = useState<string | null>(null);
   const fileRef = useRef<HTMLInputElement>(null);
 
+  async function openAttachment(att: MailAttachment): Promise<void> {
+    try {
+      const url = await download(att);
+      window.open(url, '_blank', 'noopener,noreferrer');
+    } catch (err) {
+      setAttachErr(err instanceof Error ? err.message : String(err));
+    }
+  }
+
   async function pick(e: React.ChangeEvent<HTMLInputElement>): Promise<void> {
     const file = e.target.files?.[0];
     e.target.value = '';
@@ -176,7 +185,13 @@ export function MailReader({ threadId, subject }: { threadId: string; subject: s
               <div className="miu-mail-text">{m.text}</div>
             ) : null}
             {m.attachment ? (
-              <span className="miu-attach-chip">📎 {m.attachment.filename ?? 'attachment'}{m.attachment.sizeBytes ? ` · ${fmtBytes(m.attachment.sizeBytes)}` : ''}</span>
+              canDownload ? (
+                <button type="button" className="miu-attach-chip miu-attach-dl" onClick={() => void openAttachment(m.attachment!)} title="Download">
+                  📎 {m.attachment.filename ?? 'attachment'}{m.attachment.sizeBytes ? ` · ${fmtBytes(m.attachment.sizeBytes)}` : ''} ↓
+                </button>
+              ) : (
+                <span className="miu-attach-chip">📎 {m.attachment.filename ?? 'attachment'}{m.attachment.sizeBytes ? ` · ${fmtBytes(m.attachment.sizeBytes)}` : ''}</span>
+              )
             ) : null}
           </article>
         ))}