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, 3 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
index 6ffd1c7..9c743ac 100644
--- a/.gitignore
+++ b/.gitignore
@@ -33,6 +33,9 @@ Thumbs.db
 *.db-shm
 *.db-wal
 
+# Relay data
+relay.db*
+
 # Config (may contain secrets)
 config.yaml
 config.yml