feat: add relay server and test client

Server (cmd/relay):
- gRPC server on :50051 (configurable)
- SQLite database (default: relay.db)
- Graceful shutdown on SIGTERM/SIGINT

Test client (cmd/testclient):
- Generates key
- Publishes event
- Queries events back

Build:
- make build (relay)
- make build-client (test client)
- make build-all (both)

2 files changed, 141 insertions, 0 deletions

diff --git a/cmd/relay/main.go b/cmd/relay/main.go
new file mode 100644
index 0000000..3db466d
--- /dev/null
+++ b/cmd/relay/main.go
@@ -0,0 +1,56 @@
+package main
+
+import (
+        "flag"
+        "log"
+        "net"
+        "os"
+        "os/signal"
+        "syscall"
+
+        "google.golang.org/grpc"
+
+        pb "northwest.io/nostr-grpc/api/nostr/v1"
+        grpchandler "northwest.io/nostr-grpc/internal/handler/grpc"
+        "northwest.io/nostr-grpc/internal/storage"
+)
+
+func main() {
+        var (
+                grpcAddr = flag.String("grpc-addr", ":50051", "gRPC server address")
+                dbPath   = flag.String("db", "relay.db", "SQLite database path")
+        )
+        flag.Parse()
+
+        store, err := storage.New(*dbPath)
+        if err != nil {
+                log.Fatalf("failed to create storage: %v", err)
+        }
+        defer store.Close()
+
+        handler := grpchandler.NewServer(store)
+
+        lis, err := net.Listen("tcp", *grpcAddr)
+        if err != nil {
+                log.Fatalf("failed to listen: %v", err)
+        }
+
+        grpcServer := grpc.NewServer()
+        pb.RegisterNostrRelayServer(grpcServer, handler)
+
+        log.Printf("gRPC server listening on %s", *grpcAddr)
+        log.Printf("Database: %s", *dbPath)
+
+        sigChan := make(chan os.Signal, 1)
+        signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
+
+        go func() {
+                <-sigChan
+                log.Println("Shutting down...")
+                grpcServer.GracefulStop()
+        }()
+
+        if err := grpcServer.Serve(lis); err != nil {
+                log.Fatalf("failed to serve: %v", err)
+        }
+}
diff --git a/cmd/testclient/main.go b/cmd/testclient/main.go
new file mode 100644
index 0000000..571751e
--- /dev/null
+++ b/cmd/testclient/main.go
@@ -0,0 +1,85 @@
+package main
+
+import (
+        "context"
+        "flag"
+        "log"
+        "time"
+
+        "google.golang.org/grpc"
+        "google.golang.org/grpc/credentials/insecure"
+
+        pb "northwest.io/nostr-grpc/api/nostr/v1"
+        "northwest.io/nostr-grpc/internal/nostr"
+)
+
+func main() {
+        addr := flag.String("addr", "localhost:50051", "relay address")
+        flag.Parse()
+
+        conn, err := grpc.NewClient(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()))
+        if err != nil {
+                log.Fatalf("failed to connect: %v", err)
+        }
+        defer conn.Close()
+
+        client := pb.NewNostrRelayClient(conn)
+        ctx := context.Background()
+
+        key, err := nostr.GenerateKey()
+        if err != nil {
+                log.Fatalf("failed to generate key: %v", err)
+        }
+
+        log.Printf("Generated key: %s", key.Npub())
+
+        event := &nostr.Event{
+                PubKey:    key.Public(),
+                CreatedAt: time.Now().Unix(),
+                Kind:      1,
+                Tags:      nostr.Tags{},
+                Content:   "Hello from gRPC client!",
+        }
+
+        if err := key.Sign(event); err != nil {
+                log.Fatalf("failed to sign event: %v", err)
+        }
+
+        pbEvent := &pb.Event{
+                Id:        event.ID,
+                Pubkey:    event.PubKey,
+                CreatedAt: event.CreatedAt,
+                Kind:      int32(event.Kind),
+                Tags:      []*pb.Tag{},
+                Content:   event.Content,
+                Sig:       event.Sig,
+        }
+
+        log.Println("Publishing event...")
+        resp, err := client.PublishEvent(ctx, &pb.PublishEventRequest{Event: pbEvent})
+        if err != nil {
+                log.Fatalf("failed to publish: %v", err)
+        }
+
+        if resp.Accepted {
+                log.Printf("✓ Event published successfully: %s", event.ID)
+        } else {
+                log.Printf("✗ Event rejected: %s", resp.Message)
+                return
+        }
+
+        log.Println("Querying events...")
+        queryResp, err := client.QueryEvents(ctx, &pb.QueryRequest{
+                Filters: []*pb.Filter{
+                        {Authors: []string{key.Public()}},
+                },
+        })
+        if err != nil {
+                log.Fatalf("failed to query: %v", err)
+        }
+
+        log.Printf("Found %d events", len(queryResp.Events))
+        for _, e := range queryResp.Events {
+                log.Printf("  - %s: %s", e.Id[:16], e.Content)
+        }
+}