Fix N+1 query in list_claims attestation summary

[glandua]

Summary

claims_router.py:list_claims() (line ~543) executes a separate _get_attestation_summary() query for each claim in the result set — an N+1 query pattern. With the default limit of 50, this means 51 DB roundtrips instead of 1.

Proposed Fix

Replace the per-claim loop with a single query using LEFT JOIN + GROUP BY:

SELECT c.*, er.entity_text AS claimant_name,
       COUNT(a.id) AS att_count,
       jsonb_object_agg(a.verdict, a.cnt) FILTER (WHERE a.verdict IS NOT NULL) AS att_summary
FROM claims c
LEFT JOIN entity_registry er ON c.claimant_uri = er.fuseki_uri
LEFT JOIN (
    SELECT claim_rid, verdict, COUNT(*) AS cnt
    FROM claim_attestations
    GROUP BY claim_rid, verdict
) a ON a.claim_rid = c.claim_rid
{where}
GROUP BY c.claim_rid, er.entity_text
ORDER BY c.created_at DESC
LIMIT ... OFFSET ...

Impact

Performance improvement for claim listing, especially as dogfooding scales beyond 49 claims. No API contract change.