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)

1 files changed, 7 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index d01b68b..87ede58 100644
--- a/Makefile
+++ b/Makefile
@@ -20,6 +20,13 @@ test:
 build:
         go build -o bin/relay ./cmd/relay
 
+# Build test client
+build-client:
+        go build -o bin/testclient ./cmd/testclient
+
+# Build everything
+build-all: build build-client
+
 # Clean generated files
 clean:
         rm -rf api/