Slate v2 Op-family Eleventh Slice

Supporting plan. For current queue and roadmap truth, see master-roadmap.md.

Goal

• Land the first honest delete family cut in slate: exact { at: Path } support only.

Finding

• The docs already listed Transforms.delete(...).
• The package still had no helper at all.
• The smallest honest cut was exact path deletion over the existing node ops, not broad legacy delete semantics.

Slice

• Add narrow Transforms.delete(editor, { at: Path }).
• Reuse the existing remove_node seam.
• Keep it narrow:
  • no point/range deletion
  • no unit/distance/reverse/hanging semantics
  • no fake legacy parity

Verification

• yarn mocha --require ./config/babel/register.cjs ./packages/slate/test/snapshot-contract.ts
• yarn test:mocha
• yarn workspace slate-react run test
• targeted tsc diagnostics on changed packages/slate files: 0 errors
• targeted yarn exec eslint on changed packages/slate files
• yarn prettier --check on changed slate-v2 files
• pnpm exec prettier --check on changed plate-2 docs