feat(mail): email attachments over SMTP

Email can now carry attachments (e.g. an invoice PDF). The kernel already stored
attachments as message parts + the media StoragePort holds the bytes; the gap was
the email envelope.

- EMAIL payload carries attachment REFS ({filename, contentRef, mimeType}), not
  bytes — the ledger + T8 PII redaction stay small; bytes are fetched at send time.
- SmtpProvider takes an AttachmentResolver; resolves each ref via storage and attaches
  (nodemailer). FAILS CLOSED if a declared attachment can't be resolved (or no resolver
  is wired) — never send a receipt/invoice missing its file; a FAILED command retries.
- CapabilityProviderRegistry injects the resolver from STORAGE_PORT (@Optional);
  MediaModule exports STORAGE_PORT, CapabilityModule imports MediaModule. No cycle.
- TemplatedSender + MailService + the /v1/mail/send DTO pass attachments through.

Verified: 6 new unit tests (attach, fail-closed x2, plain-unaffected, resolver,
pass-through) + a REAL Ethereal SMTP send WITH a PDF attachment (SENT). Full suite
294/294, boundary + build clean.

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

packages/iios-service/src/mail/mail.controller.ts

@@ -36,6 +36,7 @@ export class MailController {
       ...(body.locale ? { locale: body.locale } : {}),
       idempotencyKey: body.idempotencyKey,
       ...(body.purpose ? { purpose: body.purpose } : {}),
+      ...(body.attachments && body.attachments.length > 0 ? { attachments: body.attachments } : {}),
       ...(body.mirrorToUserId ? { mirrorToUserId: body.mirrorToUserId } : {}),
     });
   }