feat: add reversible human review

[SerDrozd]

Summary

Make human review decisions reversible while preserving the one-to-one matching invariant and the audit trail.

Changes

• reopen confirmed review decisions back to review
• unlink manual matches back into two unmatched rows
• restore rejected proposals when both original rows are still unmatched
• preserve the original score and evidence for rejected proposals
• record reopen, unlink, and restore actions in review history
• add a backward-compatible SQLite migration for stored review evidence
• expose reversible actions in the results UI only when the transition is valid
• prevent stale rejection events from being restored after a newer rejection of the same pair

Validation

• uv run ruff check .
• uv run mypy src tests
• uv run pytest - 69 passed
• uv build
• git diff main...HEAD --check