fix: convert Instant to Timestamp for JDBC agent metrics query

PostgreSQL JDBC driver can't infer SQL type for java.time.Instant.
Convert from/to parameters to java.sql.Timestamp before binding.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-app/src/main/java/com/cameleer3/server/app/controller/AgentMetricsController.java

@@ -5,6 +5,7 @@ import com.cameleer3.server.app.dto.MetricBucket;
 import org.springframework.jdbc.core.JdbcTemplate;
 import org.springframework.web.bind.annotation.*;
 
+import java.sql.Timestamp;
 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
 import java.util.*;
@@ -58,7 +59,7 @@ public class AgentMetricsController {
             double value = rs.getDouble("avg_value");
             result.computeIfAbsent(metricName, k -> new ArrayList<>())
                   .add(new MetricBucket(bucket, value));
-        }, intervalStr, agentId, from, to, namesArray);
+        }, intervalStr, agentId, Timestamp.from(from), Timestamp.from(to), namesArray);
 
         return new AgentMetricsResponse(result);
     }