Feat/defkit documentation

[roguepikachu]

Description of your changes

I have:

• Read and followed KubeVela's contribution process.
• Update sidebar.js if adding a new page.
• Run yarn start to ensure the changes has taken effect.

Special notes for your reviewer

---

Summary by cubic

Adds comprehensive documentation for the defkit Go SDK so platform engineers can author KubeVela X-Definitions in Go with clear guides, examples, and CLI workflows. Also adds a new Array Builder guide to help build mixed arrays in templates.

• New Features

  • New docs: overview, components, traits, policies, workflow steps, parameters, templates/resources, health/status, placement, testing.
  • Expanded Templates and Resources with the Array Builder guide (Item, ItemIf, ForEach/Guarded, ForEachWith, ArrayConcat) and examples with generated CUE.
  • Sidebar updated to surface the new defkit documentation group.

• Dependencies

  • Refreshed yarn.lock to align with documentation changes.

^{Written for commit cccf646. Summary will update on new commits.}

[roguepikachu]

Outdated. Defkit docs have been merged.