clavitor.ai: Add error logging for currency row scan failures

Fixes Cardinal Rule violation - every if needs an else.
Adds unique error code ERR-ADMIN-003 for scan failures.

fixes #13

clavitor.ai/main.go

@@ -1147,7 +1147,8 @@ Entries:
 		for rows.Next() {
 			var c Currency
 			if err := rows.Scan(&c.Code, &c.Name, &c.Symbol, &c.SymbolPosition); err != nil {
-				continue // Skip malformed rows
+				log.Printf("ERR-ADMIN-003: Failed to scan currency row - %v", err)
+				continue
 			}
 			if topMap[c.Code] {
 				top = append(top, c)