[codex] Route pre-Agon memo readiness owner-first

[8Dionysus]

Summary

• add an owner-layer shortlist hint for pre-Agon memory pressure that routes first to aoa-memo memo registry and PRE_AGON_MEMORY_READINESS.md
• document that the routing hint is not proof, KAG policy, live memory state, or routing-owned authority
• add a contract-style builder test for the new owner-first hint

Validation

• python scripts/validate_router.py
• python scripts/build_router.py --check
• python -m pytest -q tests (181 passed)
• python scripts/build_two_stage_skill_router.py --routing-root . --skills-root ../aoa-skills --check
• python scripts/validate_two_stage_skill_router.py --routing-root . --skills-root ../aoa-skills
• python scripts/release_check.py
• git diff --check