Slate v2 Phase 9 Markdown Family

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

Goal

Sharpen the markdown family from a vague later-bucket into an explicit comparison-only family.

Scope

• add legacy-only comparison rows for:
  • markdown-preview
  • markdown-shortcuts
• update the family ledger and top-level docs if those rows land cleanly

Constraints

• no fake current v2 markdown family claim
• no markdown implementation batch hidden inside the matrix
• keep the slice evidence-driven

Progress

• added legacy-only comparison rows for:
  • markdown-preview
  • markdown-shortcuts
• proved the expanded matrix through the cross-repo local runner
• split the markdown family out of the vague later bucket in the family ledger
• synced the scoreboard and top-level roadmap/docs
• verification:
  • bash ./scripts/run-cross-repo-local.sh 3010 /examples/rich-inline ../slate 3210 /examples/markdown-shortcuts "yarn build:slate-browser:playwright && yarn exec playwright test playwright/integration/examples/replacement-compatibility.test.ts --project=chromium --workers=1"