fix: resolve golangci-lint issues (gofmt, errcheck)

- Fix gofmt alignment in admin_service.go and trailing newline in
  antigravity_credits_overages.go
- Suppress errcheck for fmt.Sscanf in client.go GetMinimumAmount

backend/internal/pkg/antigravity/client.go

@@ -172,7 +172,7 @@ func (c *AvailableCredit) GetAmount() float64 {
 		return 0
 	}
 	var value float64
-	fmt.Sscanf(c.CreditAmount, "%f", &value)
+	_, _ = fmt.Sscanf(c.CreditAmount, "%f", &value)
 	return value
 }
 
@@ -182,7 +182,7 @@ func (c *AvailableCredit) GetMinimumAmount() float64 {
 		return 0
 	}
 	var value float64
-	fmt.Sscanf(c.MinimumCreditAmountForUsage, "%f", &value)
+	_, _ = fmt.Sscanf(c.MinimumCreditAmountForUsage, "%f", &value)
 	return value
 }
 

backend/internal/service/antigravity_credits_overages.go

@@ -232,4 +232,3 @@ func (s *AntigravityGatewayService) handleCreditsRetryFailure(
 			prefix, modelKey, account.ID, creditsStatusCode, reqErr, truncateForLog(creditsRespBody, 200))
 	}
 }
-