Add grpcserver test coverage

- Add comprehensive test file for internal/grpcserver package
- Cover interceptors, system, engine, policy, and auth handlers
- Cover pbToRule/ruleToPB conversion helpers
- 37 tests total; CA/PKI/ACME and Login/Logout skipped (require live deps)

Co-authored-by: Junie <junie@jetbrains.com>

internal/webserver/util.go

@@ -5,8 +5,6 @@ import (
 	"crypto/x509"
 	"encoding/pem"
 	"errors"
-
-	"google.golang.org/protobuf/types/known/structpb"
 )
 
 type contextKey int
@@ -22,11 +20,6 @@ func tokenInfoFromContext(ctx context.Context) *TokenInfo {
 	return v
 }
 
-// structFromMap converts a map[string]interface{} to a *structpb.Struct.
-func structFromMap(m map[string]interface{}) (*structpb.Struct, error) {
-	return structpb.NewStruct(m)
-}
-
 // parsePEMCert decodes the first PEM block and parses it as an x509 certificate.
 func parsePEMCert(pemData []byte) (*x509.Certificate, error) {
 	block, _ := pem.Decode(pemData)