[promote persona-mention 2/3] Wire into ring-pins + deploy + bootstrap

[don-petry]

Part of Epic #781. Blocked by the SOAK story (#783) — only after #1 cuts the tier tags, or compliance demands a pin to a nonexistent tag.

dev-lead-implementable. Three edits, each with tests:

• scripts/lib/ring-pins.sh — add persona-mention to RING_REUSABLES (compliance enforces @persona-mention/v1-<tier> per repo; deploy knows the tier).
• scripts/deploy-standard-workflows.sh — add persona-mention.yml to the deployed set, pinned per ring_tier_for_repo.
• scripts/bootstrap-new-repo.sh — seed persona-mention.yml so new repos auto-onboard at creation.

Acceptance: dry-run deploy shows incubator would get persona-mention.yml@persona-mention/v1-stable; bootstrap dry-run for a fresh repo includes it; tests green. Do not label dev-lead until #783 is done.