feat: Task Type Reference: field-level breakdown (required/optional) for IntelliSense schema

[lornakelly]

Description

Produce a definitive reference document with every task type defined in the spec (call, do, emit, for, fork, listen, raise, run, set, switch, try, wait) with for each one:

• Type name - the discriminator value as it appears in YAML/JSON
• Required fields - field name, expected type, default (if any), short description
• Optional fields - field name, expected type, default (if any), short description
• Notes/edge cases - nesting rules, mutually exclusive fields,

Motivation

IntelliSense (per #211) needs to know, at any position inside a task node, which fields are valid, which are mandatory, and what type/shape they expect.

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.