feat: Bump sdk package to alpha5

[lornakelly]

Description

Once open-workflow-specification/sdk-typescript#289 is merged, update our SDK dependency to 1.0.3-alpha5 and adapt the diagram editor to the new changes.

Motivation

Index-based node IDs currently churn whenever a sibling task is added or removed, which breaks anything in the editor that keys off node ID stability. The new name-path ID scheme fixes that at the source. Since this is a breaking SDK change, we need a deliberate upgrade pass rather than a silent bump.

Proposed Implementation

No response

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.