[DevTask] Fix workflow store interface

- `WorkflowStore` is a public interface to describe the pinia store
- It is/was required for this store as the Zod types and/or Vue ref unwrapping end up exceeding a hard limit on TypeScript type complexity
- `useWorfklowStore` no longer returns an object that accurately represents the public interface `WorkflowStore` (type assertions are used)

These should be audited and cleaned up at some point. A solution may be to split the workflow store into smaller parts.

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