Update API specifications with fern api update

[github-actions]

Update API specifications by running fern api update.

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Note

Low Risk
Spec-only sync with additive diagram fields; the parentId minLength change may affect clients that sent empty strings instead of null.

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

Diagram connections now expose an optional breakpoints array (up to 100 {x, y} points) on DiagramConnection, DiagramConnectionPartial, and DiagramConnectionRequired. The spec states breakpoints apply only to square line shapes, must form a valid orthogonal path, and are rejected for other line shapes.

Model objects tighten parentId: when present as a string it must have minLength: 1 (empty strings are invalid); null remains allowed for root-level objects. This appears across the partial, required, and full model object schemas.

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