Slate v2 Phase 9 Code Highlighting Matrix

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

Goal

Widen the decoration/highlight family in the replacement matrix with a legacy code-highlighting row.

Scope

• add one legacy code-highlighting row
• sync the decoration/highlight family docs if it lands cleanly

Constraints

• no fake direct parity claim with current highlighted-text
• keep the row family-level and evidence-driven
• verify through the cross-repo local runner on current port 3010

Progress

• added one legacy code-highlighting row to the replacement compatibility matrix
• proved the row through the cross-repo local runner
• synced the scoreboard and decoration-family docs so the landed Phase 9 slice is visible in the roadmap stack
• verification:
  • bash ./scripts/run-cross-repo-local.sh 3010 /examples/highlighted-text ../slate 3210 /examples/code-highlighting "yarn build:slate-browser:playwright && yarn exec playwright test playwright/integration/examples/replacement-compatibility.test.ts --project=chromium --workers=1"