fix(worker): 将 Gemini 同步请求交由异步队列执行

将非流式 Gemini generateContent 改为 River Worker 执行，API 通过批量状态查询等待完成，避免高并发同步请求耗尽 API 数据库连接池。\n\n生成图片在持久化时保存带哈希的资产引用，响应恢复时下载并校验后重建 Base64，数据库不保存媒体原文。请求体物化增加前置内存门禁，并扩展双 API/Worker PostgreSQL 压力测试。\n\n验证：go test ./... -count=1；go vet ./...；pnpm openapi；迁移安全检查；64 与 256 请求双角色异步 Gemini 压力测试。

apps/api/internal/runner/binary_results_test.go

@@ -2,9 +2,13 @@ package runner
 
 import (
 	"context"
+	"crypto/sha256"
 	"encoding/base64"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"strings"
@@ -112,6 +116,45 @@ func TestMaterializeAndHydrateLocalBinaryResult(t *testing.T) {
 	}
 }
 
+func TestHydrateGeneratedResultAssetReference(t *testing.T) {
+	payload := []byte("verified generated image bytes")
+	digest := sha256.Sum256(payload)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "image/png")
+		_, _ = w.Write(payload)
+	}))
+	defer server.Close()
+
+	reference := func(hash string) map[string]any {
+		return map[string]any{
+			"assetRef": map[string]any{
+				"sha256":      hash,
+				"contentType": "image/png",
+				"size":        len(payload),
+				"url":         server.URL + "/generated.png",
+			},
+			"assetStorage": map[string]any{
+				"scene":  store.FileStorageSceneImageResult,
+				"source": "b64_json",
+			},
+		}
+	}
+	service := &Service{}
+	result := map[string]any{"data": []any{map[string]any{"b64_json": reference(hex.EncodeToString(digest[:]))}}}
+	hydrated, err := service.HydrateTaskResult(context.Background(), "task-remote", result)
+	if err != nil {
+		t.Fatalf("hydrate generated result asset: %v", err)
+	}
+	item := hydrated["data"].([]any)[0].(map[string]any)
+	if got, want := item["b64_json"], base64.StdEncoding.EncodeToString(payload); got != want {
+		t.Fatalf("hydrated Base64=%v, want %v", got, want)
+	}
+
+	result = map[string]any{"data": []any{map[string]any{"b64_json": reference(strings.Repeat("0", 64))}}}
+	_, err = service.HydrateTaskResult(context.Background(), "task-corrupted", result)
+	assertClientErrorCode(t, err, "binary_result_corrupted")
+}
+
 func TestHydrateLocalBinaryResultReturnsExpiredAndCorruptedErrors(t *testing.T) {
 	service := newLocalBinaryTestService(t)
 	service.cfg.LocalResultTTLHours = 1