fix: Add created_at to existing_claim CTE to fix PostgreSQL error

Error:
- column "created_at" does not exist
- There is a column named "created_at" in table "clpr_claims", but it cannot be referenced from this part of the query

Root Cause:
- existing_claim CTE only selected id and payload
- But INSERT query tried to use: (SELECT created_at FROM existing_claim)
- PostgreSQL couldn't find created_at in existing_claim CTE

Solution:
- Added created_at to existing_claim CTE SELECT clause
- Now created_at is available for use in INSERT query

Files:
- docs/SQL_CLAIMSAVE_UPSERT_SIMPLE.sql: Added created_at to existing_claim CTE

docs/SQL_CLAIMSAVE_UPSERT_SIMPLE.sql

@@ -19,7 +19,8 @@ WITH partial AS (
 existing_claim AS (
   SELECT 
     id,
-    payload
+    payload,
+    created_at
   FROM clpr_claims
   WHERE id = (SELECT claim_id_str::uuid FROM partial)
      OR payload->>'claim_id' = (SELECT claim_id_str FROM partial)