- Add Attachment ORM model (id, conversation_id, message_id, filename, content_type, blob_url, size_bytes, created_at) with FK to conversations
- Add POST /api/attachments/upload (multipart, 50MB limit), GET /api/attachments/{id}, GET /api/attachments/{id}/download (302 to SAS URL), DELETE /api/attachments/{id}
- Add delete_blob() and generate_sas_url() to storage/blob.py for download redirect and cleanup
- Dispatch parse_attachment task to Service Bus for parseable types (PDF, images, CSV, DOCX, XLSX)
- Pre-create blob container on startup (best-effort)
- Add AttachmentOut schema and full API docs in doc/api.md
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
