Update API specifications with fern api update

[github-actions]

Update API specifications by running fern api update.

---

Note

Medium Risk
OpenAPI-only, but the parentId minLength rule can reject previously accepted empty-string parent IDs, and the new breakpoints field documents server validation clients must honor for square connections.

Overview
Regenerates openapi.json from Fern to document two API contract updates.

Diagram connections now expose an optional breakpoints array on DiagramConnection, DiagramConnectionPartial, and DiagramConnectionRequired. Each entry is an { x, y } waypoint (up to 100), ordered from origin to target. The spec states breakpoints apply only when lineShape is square, are ignored/rejected for other shapes, and must form a valid orthogonal path (shared x or y between consecutive points, no duplicates, right-angle corners only).

Model objects tighten parentId: non-null values must have minLength: 1, so empty strings are invalid while null remains allowed for root-level objects (applied across the related partial/required/full schemas in the diff).

^{Reviewed by Cursor Bugbot for commit 9b21e6a. Bugbot is set up for automated code reviews on this repo. Configure here.}