Update: teach shipped SpecSync 6.0 in the catalog skill

[0xLeif]

Summary

• Teach shipped SpecSync 6.0 in the shared catalog spec-sync skill instead of the RC-era workflow.
• Prefer 6.0.0 from cargo or GitHub Releases (Homebrew may still lag on 5.2.0); 6.0.0 is Latest.
• Encode: specsync check is the product; SDD is opt-in via specsync change adopt.
• When adopted, one path: new → answer → approve --actor → implement → change check --commit → review --reviewer → ship/finalize. Do not commit between review and ship. Merge on GitHub; SpecSync does not merge.
• Slug ids (not CHG-NNNN), same actor may approve and review, v1 start/verify/accept/archive are recovery only.
• Action consumers: uses: CorvidLabs/spec-sync@v6.0.0 with version: '6.0.0' (tagged Action default is still 6.0.0-rc.14).
• Catalog skill is principles; never overwrite a generated local skill.
• Routing skill drops preferred-RC language and points at spec-sync instead of restating the path.

Test Plan

• fledge lanes run verify on the committed tree
• Hosted CI green on this PR