Make manual review persistence durable

[shiny-code-bot]

Summary

• make manual persisted reviews claim a review snapshot epoch and persist Pending before entering review mode
• cancel/supersede existing background review state before durable manual review startup
• drop persistence for the manual review if the durable start cannot be recorded, avoiding misleading partial run records
• add regression coverage for completed/cancelled manual runs and background-to-manual durable handoff

Verification

• cargo fmt --all -- --check
• git diff --check
• just test -p codex-core review_op_with_persistence_writes_auto_review_run review_op_with_persistence_writes_cancelled_run_when_interrupted manual_review_with_persistence_supersedes_running_background_review
• focused read-only agent review: no blocking issues

Notes

Background auto-review for this branch did not produce semantic findings because the current diff exceeded the configured review size limit. Focused review agents and targeted tests covered the changed lifecycle path.