fix(api): resolve legacy approval batch shares

[federicodeponte]

Summary

• routes legacy standalone approval batch share rows through the public batch payload without reloading through the canonical share_links repository
• keeps canonical revoked/expired share_links rejection intact for both /approvals/public-batch and /s
• updates regression coverage for the legacy /s fallback

Verification

• cd apps/api && python3 -m pytest tests/test_approvals_batch_share_link.py -q
• 19 passed, 1 warning in 30.44s