fix(antigravity): use official daily endpoint

Align the daily Cloud Code host with the current Antigravity client so requests do not use the legacy sandbox hostname.

backend/internal/pkg/antigravity/oauth.go

@@ -54,7 +54,7 @@ const (
 
 	// Antigravity API 端点
 	antigravityProdBaseURL  = "https://cloudcode-pa.googleapis.com"
-	antigravityDailyBaseURL = "https://daily-cloudcode-pa.sandbox.googleapis.com"
+	antigravityDailyBaseURL = "https://daily-cloudcode-pa.googleapis.com"
 )
 
 var userAgentVersionPattern = regexp.MustCompile(`^\d+\.\d+\.\d+$`)

backend/internal/pkg/antigravity/oauth_test.go

@@ -94,6 +94,9 @@ func TestForwardBaseURLs_Daily优先(t *testing.T) {
 	if len(urls) == 0 {
 		t.Fatal("ForwardBaseURLs 返回空列表")
 	}
+	if antigravityDailyBaseURL != "https://daily-cloudcode-pa.googleapis.com" {
+		t.Fatalf("daily URL 未与官方客户端对齐: got %s", antigravityDailyBaseURL)
+	}
 
 	// daily URL 应排在第一位
 	if urls[0] != antigravityDailyBaseURL {