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/inbox/adapter.ts

@@ -1,4 +1,4 @@
-import type { InboxItem, InboxState, MailMessage, MailPerson } from './types';
+import type { MailAttachment, InboxItem, InboxState, MailMessage, MailPerson } from './types';
 
 /**
  * The inbox seam. A host implements this; the SDK renders it. Mirrors MessagingAdapter's philosophy:
@@ -15,14 +15,18 @@ export interface InboxAdapter {
   /** Messages of one mail thread (HTML + text parts) for the reader. */
   mailHistory(threadId: string): Promise<MailMessage[]>;
 
-  /** Reply into an existing mail thread. */
-  mailReply(threadId: string, content: string): Promise<void>;
+  /** Reply into an existing mail thread, optionally with one attachment. */
+  mailReply(threadId: string, content: string, attachment?: MailAttachment): Promise<void>;
+
+  // ── Attachments (optional) — absent hides the attach affordance ──
+  /** Upload a file to storage, returning a reference to send with a reply/compose. */
+  uploadAttachment?(file: File): Promise<MailAttachment>;
 
   // ── Compose (optional) — absent hides the "New message" affordance ──
   /** People you can compose an in-app message to. */
   directory?(): Promise<MailPerson[]>;
   /** App-to-app mail (no SMTP) to a registered user's in-app inbox. */
-  composeInternal?(recipientUserId: string, subject: string, text: string): Promise<void>;
+  composeInternal?(recipientUserId: string, subject: string, text: string, attachments?: MailAttachment[]): Promise<void>;
   /** External email (SMTP) to an address. */
-  composeExternal?(target: string, subject: string, text: string): Promise<void>;
+  composeExternal?(target: string, subject: string, text: string, attachments?: MailAttachment[]): Promise<void>;
 }