fix: qualify column names in PerfMetric upsert to avoid ambiguity

PostgreSQL raises 'column reference is ambiguous' (SQLSTATE 42702) on
ON CONFLICT DO UPDATE because unqualified column names match both the
target row and EXCLUDED. Prefix with the table name so the existing
value is referenced unambiguously. Compatible with MySQL and SQLite.

Closes #4683

Signed-off-by: SAY-5 <SAY-5@users.noreply.github.com>

model/perf_metric.go

@@ -37,13 +37,13 @@ func UpsertPerfMetric(metric *PerfMetric) error {
 			{Name: "bucket_ts"},
 			{Name: "bucket_ts"},
 		},
 		},
 		DoUpdates: clause.Assignments(map[string]interface{}{
 		DoUpdates: clause.Assignments(map[string]interface{}{
-			"request_count":    gorm.Expr("request_count + ?", metric.RequestCount),
-			"success_count":    gorm.Expr("success_count + ?", metric.SuccessCount),
-			"total_latency_ms": gorm.Expr("total_latency_ms + ?", metric.TotalLatencyMs),
-			"ttft_sum_ms":      gorm.Expr("ttft_sum_ms + ?", metric.TtftSumMs),
-			"ttft_count":       gorm.Expr("ttft_count + ?", metric.TtftCount),
-			"output_tokens":    gorm.Expr("output_tokens + ?", metric.OutputTokens),
-			"generation_ms":    gorm.Expr("generation_ms + ?", metric.GenerationMs),
+			"request_count":    gorm.Expr("perf_metrics.request_count + ?", metric.RequestCount),
+			"success_count":    gorm.Expr("perf_metrics.success_count + ?", metric.SuccessCount),
+			"total_latency_ms": gorm.Expr("perf_metrics.total_latency_ms + ?", metric.TotalLatencyMs),
+			"ttft_sum_ms":      gorm.Expr("perf_metrics.ttft_sum_ms + ?", metric.TtftSumMs),
+			"ttft_count":       gorm.Expr("perf_metrics.ttft_count + ?", metric.TtftCount),
+			"output_tokens":    gorm.Expr("perf_metrics.output_tokens + ?", metric.OutputTokens),
+			"generation_ms":    gorm.Expr("perf_metrics.generation_ms + ?", metric.GenerationMs),
 		}),
 		}),
 	}).Create(metric).Error
 	}).Create(metric).Error
 }
 }