v0.21.0

Changed

• The agent-host substrate now lives in
  django-pydantic-agent, a new
  settings-agnostic package this release depends on. Agent construction, the tool
  registry, toolset/capability composition, audit, the tool guard, user resolution,
  the storage contracts and the reference store models moved there; this package
  keeps the AG-UI transport — the view, the SSE stream, AGUIServer.urls, the
  browser-facing sub-views, skills and transcription. It is the lift-down that lets
  a second transport share one substrate.

  The public surface is unchanged: every moved symbol is permanently
  re-exported, so from django_ag_ui import ToolRegistry (and friends) keeps
  working and downstream projects need only a version bump.

Breaking

• INSTALLED_APPS: the reference store app moved — replace
  "django_ag_ui.contrib.store" with "django_pydantic_agent.contrib.store".
• The model stores no longer read DJANGO_AG_UI["ALLOW_ANONYMOUS"]. A
  settings-agnostic substrate cannot read a transport's settings key, so pass
  allow_anonymous=True to the store constructor instead.
• Conversation.messages holds JSON-serialisable records, not ag_ui Message
  objects. The substrate persists transport-owned records verbatim (client
  message ids survive untouched) and the AG-UI wire shape is converted at this
  package's boundary. Code that read message.content off a loaded conversation
  now reads message["content"]; messages_to_jsonable / messages_from_jsonable
  live in django_ag_ui.persistence.utils.
• The attachment toolset's internal id is now django-pydantic-agent-attachments.
  Tool names (read_attachment) and the wire are unaffected.