Implement notifications service with shared messaging and email drivers (#36)

.gitignore

@@ -29,3 +29,8 @@ pnpm-debug.log*
 # Local BFF configuration and build output
 /backend/config.yml
 /backend/bff
+
+# Protobuf client bindings are generated, never committed.
+/backend/notifications/interface/notifications/**/*.pb.go
+/backend/notifications/config.yml
+/backend/notifications/notifications