Slate v2 Core Docs Truth Pass

Goal

Align the high-signal core concepts and API pages with the recovered live surface instead of leaving old Slate signatures in the docs.

Completed

• updated the core concepts pages:
  • concepts/01-interfaces.md
  • concepts/02-nodes.md
  • concepts/03-locations.md
  • concepts/07-editor.md
• updated the main editor reference page:
  • api/nodes/editor.md
• corrected stale examples and signatures around:
  • children: Descendant[]
  • current marks shape
  • onChange()
  • delete option objects
  • insertFragment(...)
  • insertNode(...)
  • Node.common(...)

Verification

• targeted grep over the docs tree for the stale signatures removed in this pass
• yarn lint:typescript