Retire every W unit to Landed — 30-slices.md moves to the kit's current format

[The-Running-Dev]

design/30-slices.md predated the kit's current slice convention (## S<n> with Status:, a ## Landed section), so get-next-slice.ts could not read it. This moves it to that format.

Changes

• design/30-slices.md (5,400 → 209 lines). Each of the 125 W units is now one Landed row: its pull requests, criteria range, and merge commit. W68 and W70 show as cancelled via Record SubZeroDev.Adventures as the play surface, and reconcile W57/W62/W67/W68/W70 #271. Each row has an <a id="wN"> anchor, so existing #wN links still resolve. Items that were still open move to Carried Forward (9 bullets). New slices are ## S<n>, numbered from S121. The full slice bodies remain at 7081402 and in plans/.
• PR numbers were checked against merged PRs. Several W Status lines cited issue numbers rather than PRs, and some title matches picked up planning/sync PRs. Both were corrected by hand.
• build/Test-Documentation.ps1 now collects inline <a id="…"> anchors as well as headings.
• site/src/roadmap/roadmapData.ts now counts non-cancelled Landed rows plus Status: done S slices. The result is still 123.
• CLAUDE.md, agent.md and docs/docs/index.md now describe the new form. The CLAUDE.md W-id clause and the one-unit Hard Rule now refer to S slices.
• design/90-decisions.md: a new 2026-10-07 entry, which supersedes the 2026-09-05 rejection.
• Regenerated: docs/docs/engine/TODO.md and design/TODO.md.

Verified

• ./build/Test-Documentation.ps1: passed (131 Markdown files; drift check across 18 generated pages and the guide).
• The anchor collector fails in both directions it should:
  • with the change reverted, #w114 fails;
  • with the change in place, a bogus #w999 fails.
• site: test 17/17, typecheck, lint and format:check all pass.
• get-next-slice.ts reports Finished.
• Advisory test-design.ts drops from 49 findings to 13. The 13 left are pre-existing false positives in 10-design / 20-contract, where path fragments such as /authoring are read as commands.
• git diff --check is clean.
• Not run locally: the Docusaurus production build, because docs.ps1 is not installed. Verify Documentation Build is the evidence for that.
• Not run: engine gates (no engine code changed).