feat: add gRPC server support (Closes #100)

[ljluestc]

Summary

Adds gRPC server support to go-gin-api, addressing #100 which reported that gRPC functionality was missing from the codebase.

Changes

New Files

• api/proto/service.proto — Protobuf definitions for HealthService and HelloService
• internal/grpc/pb/ — Generated Go protobuf + gRPC stubs (message types and server registration)
• internal/grpc/interceptor/interceptor.go — Unary server interceptors:
  • UnaryLogInterceptor — Logs every gRPC call with method name, duration, and errors (using zap)
  • UnaryRecoveryInterceptor — Recovers from panics and returns codes.Internal
• internal/grpc/service/health.go — HealthService implementation (always returns SERVING)
• internal/grpc/service/hello.go — HelloService implementation with trace ID propagation via gRPC metadata
• internal/grpc/server/server.go — gRPC server setup with chained interceptors and service registration

Modified Files

• main.go — Initializes gRPC server on :9998, runs alongside HTTP server, adds graceful shutdown hook
• configs/constants.go — Adds ProjectGRPCPort = ":9998"
• go.mod / go.sum — Adds google.golang.org/grpc v1.46.0
• README.md — Documents gRPC as an integrated component

Architecture

HTTP Server (:9999)  ──►  gin engine (existing)
gRPC Server (:9998)  ──►  grpc.Server
                           ├── HealthService.Check
                           └── HelloService.SayHello
                           Interceptors: Recovery → Logging

Testing

# Health check
grpcurl -plaintext localhost:9998 api.HealthService/Check

# Hello service
grpcurl -plaintext -d '{"name": "World"}' localhost:9998 api.HelloService/SayHello

---

Conversation link

Co-Authored-By: Oz oz-agent@warp.dev