Dedupe Auto Review runs by diff fingerprint

[shiny-code-bot]

Refs #329

Summary

• persist Auto Review diff fingerprints, changed-path metadata, and scoped paths in the run ledger
• skip launching duplicate in-flight reviews for the same base/diff and reuse completed equivalent reviews
• preserve duplicate-skipped ledger rows when the synthetic completion event is recorded

Validation

• cargo test -p code-core review_store --lib
• cargo test -p code-tui duplicate_superseded_auto_review_status_is_archived_once --features test-helpers
• cargo test -p code-tui auto_review_diff_fingerprint --features test-helpers
• ./build-fast.sh