fix: address remaining errcheck findings in s3cache and msi packager

- s3cache.go: defer func() { _ = os.Remove(tmp.Name()) }() in Restore/Store
- msi.go: defer func() { _ = os.RemoveAll(stagingDir) }()

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jasonmiller-cc

internal/cache/s3cache.go

@@ -83,7 +83,7 @@ func (c *S3Cache) Restore(ctx context.Context, key, destDir string) error {
 	if err != nil {
 		return err
 	}
-	defer os.Remove(tmp.Name())
+	defer func() { _ = os.Remove(tmp.Name()) }()
 	defer tmp.Close()
 
 	if _, err := io.Copy(tmp, out.Body); err != nil {
@@ -104,7 +104,7 @@ func (c *S3Cache) Store(ctx context.Context, key, srcDir string) error {
 	if err != nil {
 		return err
 	}
-	defer os.Remove(tmp.Name())
+	defer func() { _ = os.Remove(tmp.Name()) }()
 	defer tmp.Close()
 
 	if err := archiveDir(srcDir, tmp.Name()); err != nil {

internal/packager/msi/msi.go

@@ -42,7 +42,7 @@ func (m *MSIPackager) Pack(ctx context.Context, proj *project.Definition, instal
 	if err != nil {
 		return nil, err
 	}
-	defer os.RemoveAll(stagingDir)
+	defer func() { _ = os.RemoveAll(stagingDir) }()
 
 	if err := os.MkdirAll(outputDir, 0o755); err != nil {
 		return nil, err