[codex] Generalize main release evidence tooling

[iiwish]

Summary

• Generalize release:main-candidate:evidence from P8-only naming to stage-neutral main release-candidate evidence.
• Add agent-cli-runtime.mainReleaseCandidateEvidence.v1 to the schema inventory and docs.
• Keep existing P8 main evidence files readable as historical evidence without rewriting them or treating them as current fresh main evidence.

Validation

• git diff --check
• npm run typecheck
• npm run lint
• npm run build
• npm test
• npm run package:check
• npm run prepublish:check
• npm run release:package-content:verify -- --base-ref 21950c270882980d740120e1c1770dc1b0b98358 --head-ref HEAD

Release Evidence Boundary

P9-2 tooling commit c60d0a59b6092442e1be29941e23126a3975daa4 is not yet on origin/main at PR creation time. Fresh remote main release-candidate evidence must be generated only after this PR is merged to main; do not use the historical P8 evidence files as current P9 evidence.

No npm publish, GitHub Release creation, npm token, authenticated real-agent run, or raw workflow log evidence is included in this PR.