Plane: Unauthenticated ORM field-name injection via `group_by`/`sub_group_by` on public deploy boards (DoS + blind oracle)

Plane is an open-source project management tool. Prior to 1.4.0, the unauthenticated public issues endpoint accepts group_by and sub_group_by query parameters and passes them without an allowlist to grouped paginators, where they are used as ORM field names by F(field), .values(field), .order_by(field), and Window partition_by operations. An anonymous attacker can supply arbitrary field paths that trigger an unhandled FieldError or KeyError and an HTTP 500 response, or force the ORM to resolve __-separated relational paths as a blind traversal oracle. This is the same field-name injection class addressed by earlier order_by sanitization, but that remediation left group_by and sub_group_by unvalidated. The issue does not directly disclose column values because issue_group_values() returns an empty list for unknown fields, the result projection uses a fixed required_fields list, and the subgrouped path raises KeyError before serialization. This issue is fixed in 1.4.0.