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/grpcserver/pki.go

@@ -7,7 +7,7 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 
-	pb "git.wntrmute.dev/kyle/metacrypt/gen/metacrypt/v1"
+	pb "git.wntrmute.dev/kyle/metacrypt/gen/metacrypt/v2"
 	"git.wntrmute.dev/kyle/metacrypt/internal/engine"
 	"git.wntrmute.dev/kyle/metacrypt/internal/engine/ca"
 )