fix(flow): restore strings import and register KMS pin

- Add back strings import (still used by strings.TrimSpace)
- Register cloud.google.com/go/kms v1.24.0 in check_pinned_versions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: whites11

flow/cmd/check_pinned_versions/main.go

@@ -17,6 +17,7 @@ import (
 // To update a pinned dependency, change both go.mod AND this map.
 var pinnedVersions = map[string]string{
 	"cloud.google.com/go/bigquery":                    "v1.72.0",
+	"cloud.google.com/go/kms":                         "v1.24.0",
 	"cloud.google.com/go/pubsub/v2":                   "v2.3.0",
 	"github.com/aws/aws-sdk-go-v2/feature/s3/manager": "v1.21.0",
 	"google.golang.org/api":                           "v0.257.0",

flow/internal/env.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"reflect"
 	"strconv"
+	"strings"
 	"sync"
 
 	gcpkms "cloud.google.com/go/kms/apiv1"