v0.7.0

Added

• File uploads (server side). A new AttachmentStore Protocol
  (async, owner-scoped save / open / delete) is the persistence seam for
  files a user attaches to a conversation, set via
  DJANGO_AG_UI["ATTACHMENT_STORE"]. The package ships NullAttachmentStore
  (the default — uploads disabled, the endpoint answers 410) and an abstract
  ModelAttachmentStore base (async wrapping + owner scoping over three sync
  ops). Uploads return a lightweight AttachmentRef (id/name/mime/size),
  never bytes — the AG-UI message stream stays vanilla.
• AttachmentsView, mounted by get_urls(view, attachments=<store>) at
  <prefix>attachments/ (POST multipart upload → 201 ref) and
  <prefix>attachments/<id>/ (GET download, DELETE). Uploads are validated
  server-side against ATTACHMENT_MAX_BYTES (oversize → 413) and
  ATTACHMENT_ALLOWED_TYPES (disallowed → 415); downloads stream as an
  attachment with X-Content-Type-Options: nosniff. Every operation is
  owner-scoped — another user's id reads as 404 — with the same
  require_authenticated / get_user auth seam as DjangoAGUIView.
• read_attachment tool. When an attachment store is configured, the view
  wires a per-request read_attachment(attachment_id) tool onto the agent,
  scoped to the acting user, so the model reads a file's contents server-side
  (text inlined; binary summarised) — the bytes never ride the wire. A consumer
  that registers its own read_attachment keeps it (registry tools win).
• New settings: ATTACHMENT_STORE (dotted path, default None = off),
  ATTACHMENT_MAX_BYTES (default 10 MiB, 0 disables), and
  ATTACHMENT_ALLOWED_TYPES (default () = any).
• Reference durable file store (opt-in). The django_ag_ui.contrib.store
  app now also ships a StoredAttachment model + migration and
  DefaultAttachmentStore (a ModelAttachmentStore subclass keeping bytes in
  Django Storage — S3/GCS via STORAGES — and metadata in a row, owner-scoped
  by an opaque attachment_id). The base package still ships no model.