v2.3.0

feat: upgrade to upstream Vikunja v2.3.0 API

Updates the upstream spec from v1.0.0-rc2 to v2.3.0, bringing 15 new
endpoints and 7 new schemas:

New features:
- CSV import (detect, preview, migrate, status)
- WeKan migration (migrate, status)
- Task duplication (PUT /tasks/{id}/duplicate)
- Task read marking (POST /tasks/{id}/read)
- Task lookup by per-project index
- User-level webhooks (separate from project webhooks)
- User logout and token refresh endpoints
- Testing endpoint (DELETE /test/all)

Breaking changes (from upstream):
- Expand query parameter is now string instead of string[]
- /tasks/all renamed to /tasks
- Webhook model no longer exposes basic_auth fields or user_id
- Task model no longer exposes is_unread flag
- PasswordReset/UserPassword validation constraints removed

Adds path_based_overrides and type_name_override for the new operations
and csv.* schemas.

Version now matches upstream Vikunja API version (2.3.0).