Update API specifications with fern api update

[github-actions]

Update API specifications by running fern api update.

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Note

Medium Risk
OpenAPI contract changes affect API clients and may reject previously accepted empty parentId strings; breakpoint rules are new surface area for square connection updates.

Overview
Regenerates openapi.json from Fern to document new diagram-connection routing and tighter model-object ID validation.

Diagram connections (DiagramConnection, DiagramConnectionPartial, DiagramConnectionRequired) now expose an optional breakpoints array (up to 100 {x, y} points). The spec states breakpoints apply only when lineShape is square, must form a valid orthogonal path (no diagonals, no duplicate points, alternating horizontal/vertical segments), and are rejected for other line shapes.

Model object payloads gain minLength: 1 on parentId when it is a string (still nullable for root objects), so empty-string parent IDs are no longer valid in the published API contract.

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