Merge feature/workbench-w3-artifacts into unify/skills-20261112

Conflicts kept both sides: runner.py docstring (W2 board changes and W3 gate changes), signing.py constants (W2 STATUSES and W3 GATE_*), index.html.j2 styles (W1 diff and W3 ancestry).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/requirements/003-operator-workbench.md

@@ -219,7 +219,7 @@ flowchart TD
 
 ### W3 Artifacts
 
-- [ ] "Clean all merged" shows the gc dry run of every `merged-clean` item; one
+- [x] "Clean all merged" shows the gc dry run of every `merged-clean` item; one
       passkey runs the signed job.
 - [ ] Without a GitHub token, local branches merged by ancestry into the
       default branch and without a remote branch can be deleted; the others