Add API tokens and OAuth2 client support for external integrations

- Personal API tokens (model, user-settings UI, admin, management command,
  DRF auth class) for non-interactive API access from automations like n8n.
  Raw token shown once; only a SHA-256 hash is stored; last_used_at writes
  are throttled.
- OAuth2 authorization server via django-oauth-toolkit with authorization
  server metadata and optional, off-by-default Dynamic Client Registration
  (RFC 7591), so remote OAuth/MCP clients can authenticate and self-register.
- Tests for token auth, DCR gating and the management commands, plus
  .env.example and README documentation.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -16,6 +16,7 @@ dependencies = [
     "django-filter==25.2",
     "django-hijack==3.7.8",
     "django-import-export~=4.4.1",
+    "django-oauth-toolkit~=3.0.1",
     "django-pwa~=2.0.1",
     "django-vite==3.1.0",
     "djangorestframework~=3.17.1",