fix(gemini): 移除空返图占位并暴露失败原因

Gemini 图片响应未包含可提取资源时，不再返回伪造占位图，改为非重试失败并保留安全拦截、候选结束状态和上游错误等结构化诊断。\n\n同步将诊断写入 HTTP 错误、任务结果、attempt 指标和日志，确保任务失败时不结算，并补充单元及 PostgreSQL 验收测试。\n\n验证：gofmt、go test ./... -count=1、go vet ./...、迁移安全检查、pnpm openapi。

apps/api/internal/runner/recording.go

@@ -258,6 +258,9 @@ func failureMetrics(err error, simulated bool) (string, map[string]any, time.Tim
 		metrics["error"] = err.Error()
 		metrics["errorCategory"] = info.Category
 		metrics["retryable"] = retryable
+		if details := clients.ErrorDetails(err); len(details) > 0 {
+			metrics["errorDetails"] = details
+		}
 		if detail := rateLimitFailureDetail(err); len(detail) > 0 {
 			metrics["rateLimit"] = detail
 		}
@@ -288,6 +291,9 @@ func buildFailureResult(code string, message string, requestID string, err error
 	if requestID != "" {
 		errorPayload["requestId"] = requestID
 	}
+	if details := clients.ErrorDetails(err); len(details) > 0 {
+		errorPayload["details"] = details
+	}
 	if detail := rateLimitFailureDetail(err); len(detail) > 0 {
 		errorPayload["rateLimit"] = detail
 	}