feature: replace deprecated rollupOptions in Vite configurations #500

Description

Replace the remaining uses of build.rollupOptions with build.rolldownOptions in the repository’s vite.config.ts files.

Motivation

Vite deprecates build.rollupOptions in favor of build.rolldownOptions. The Diagram Editor already uses the replacement; the remaining configurations should follow the same approach.

Reference: https://vite.dev/config/build-options.html#build-rollupoptions

Proposed Implementation

Rename the deprecated configuration key, preserving the existing options and build behavior.

Definition of Done

• Implementation: Fully implemented according to the Open Workflow spec.
• Unit Tests: Comprehensive unit tests are included and passing.
• Integration Tests: Verified within the monorepo and target environments (Web/VS Code).
• Documentation: Updated README.md, ADRs, or official docs.
• Performance: No significant regression in editor responsiveness.
• Accessibility: UI changes comply with accessibility standards.