docs(plans): add cycle-4 production-readiness audit plans (008-013)

Commit notes

Reconcile cycle-3 (all DONE, in main) and add six new handoff plans: test clean-skip, public pack pattern cap, folder N+1, admin regen bound, CSP enforcing, and SSE token cleanup.

Co-Authored-By: Claude Opus 4.8 <[email redacted]> Claude-Session: [private session redacted]