Align auto-review store layout

[shiny-code-bot]

Summary

Align Codex Lab's durable auto-review store with the authoritative Every Code layout identified during the #126 parity audit.

This changes new auto-review state from the old unscoped per-run layout:

CODEX_LAB_HOME/auto-review/runs/<run_id>.json

to the repo-scoped layout:

CODEX_LAB_HOME/state/review/repo-<key>/auto-review/runs.json
CODEX_LAB_HOME/state/review/repo-<key>/auto-review/outputs/<run_id>.json

The store now:

• requires scoped construction via AutoReviewStore::for_scope
• writes a per-run sidecar before publishing the runs.json index
• merges sidecar records back into the index view so concurrent/stale runs.json writes do not hide runs
• uses the same repo/worktree scope for persistence, awareness injection, and app-server summary/detail endpoints

Refs #60
Refs #126

Verification

• cargo fmt --manifest-path codex-rs/Cargo.toml --all --check
• git diff --check
• cargo test -p codex-auto-review
• cargo test -p codex-core review_persistence
• cargo test -p codex-core auto_review_awareness
• cargo test -p codex-app-server suite::v2::review
• Final read-only review agent reported no findings on the current diff