- media-api: useUploadAttachment (presign → direct PUT to IIOS storage),
useDownloadUrl (short-lived signed URL), isImage, 25MB cap
- socket + REST send now carry attachment {contentRef, mimeType, sizeBytes}
- composer: 📎 attach button, staged chip, send with attachment (text optional)
- MessageBubble renders AttachmentView (inline image or file chip), aligned
to the message side; empty bubble suppressed for attachment-only messages
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
