refactor(layout): role contracts move to roles/ - root is bootstrap-only

Owner direction: the repository root holds first-class, bootstrap-required
configuration only. conductor-policy.json is a ROLE contract (the
conductor's authority), one of scores of future role contracts
(agent-policy, coder-policy, ...) - such files get a dedicated home.

- roles/conductor-policy.json (git mv)
- conductor-apply.sh + test-conductor.sh read the new path
- CONDUCTOR.md records the roles/ convention

Closes UX follow-up from owner layout review; no issue (convention change).

docs/plans/CONDUCTOR.md

@@ -2,6 +2,13 @@
 
 How the stack orchestrates headless pi workers to do work on itself.
 
+## Role contracts
+
+Role authority is declared in role contracts, one file per role, under
+`roles/` (e.g. `roles/conductor-policy.json`). The repository root holds
+only first-class, bootstrap-required configuration; role contracts are
+tracked, versioned files whose changes arrive as reviewed commits.
+
 ## Roles
 
 | Role | Runs where | Powers | Never has |