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/hooks.ts

@@ -60,6 +60,8 @@ export interface MailThreadState {
   reply: (content: string, attachment?: MailAttachment) => Promise<void>;
   canAttach: boolean;
   upload: (file: File) => Promise<MailAttachment>;
+  canDownload: boolean;
+  download: (attachment: MailAttachment) => Promise<string>;
   refetch: () => void;
 }
 
@@ -113,8 +115,25 @@ export function useMailThread(threadId: string | null): MailThreadState {
     },
     [adapter],
   );
+  const download = useCallback(
+    async (attachment: MailAttachment) => {
+      if (!adapter.downloadAttachment) throw new Error('attachment download is not supported by this adapter');
+      return adapter.downloadAttachment(attachment);
+    },
+    [adapter],
+  );
 
-  return { messages, loading, error, reply, canAttach: typeof adapter.uploadAttachment === 'function', upload, refetch };
+  return {
+    messages,
+    loading,
+    error,
+    reply,
+    canAttach: typeof adapter.uploadAttachment === 'function',
+    upload,
+    canDownload: typeof adapter.downloadAttachment === 'function',
+    download,
+    refetch,
+  };
 }
 
 export interface ComposeState {