fix: address linter issues in docs/drive commands

- Fix variable shadowing in DocsUpdateCmd (govet: shadow)
- Extract formatAuto constant to satisfy goconst linter

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/docs.go

@@ -424,7 +424,8 @@ func (c *DocsUpdateCmd) Run(ctx context.Context, kctx *kong.Context, flags *Root
 
 	insertIndex := c.Index
 	if insertIndex <= 0 {
-		doc, err := svc.Documents.Get(id).
+		var doc *docs.Document
+		doc, err = svc.Documents.Get(id).
 			Fields("documentId,body/content(startIndex,endIndex)").
 			Context(ctx).
 			Do()

internal/cmd/drive.go

@@ -52,6 +52,7 @@ const (
 	extPNG                 = ".png"
 	extTXT                 = ".txt"
 
+	formatAuto             = "auto"
 	driveShareToAnyone = "anyone"
 	driveShareToUser   = "user"
 	driveShareToDomain = "domain"
@@ -1121,7 +1122,7 @@ func guessMimeType(path string) string {
 func downloadDriveFile(ctx context.Context, svc *drive.Service, meta *drive.File, destPath string, format string) (string, int64, error) {
 	isGoogleDoc := strings.HasPrefix(meta.MimeType, "application/vnd.google-apps.")
 	normalizedFormat := strings.ToLower(strings.TrimSpace(format))
-	if normalizedFormat == "auto" {
+	if normalizedFormat == formatAuto {
 		normalizedFormat = ""
 	}
 
@@ -1244,7 +1245,7 @@ func driveExportMimeType(googleMimeType string) string {
 
 func driveExportMimeTypeForFormat(googleMimeType string, format string) (string, error) {
 	format = strings.ToLower(strings.TrimSpace(format))
-	if format == "" || format == "auto" {
+	if format == "" || format == formatAuto {
 		return driveExportMimeType(googleMimeType), nil
 	}