converge-relay: phase 1 — webhook-to-SSE relay server in Go

- Pub/sub broker with fan-out to SSE clients
- POST /webhook — receives Gitea push events, optional HMAC verification
- GET /events — SSE stream of push events
- GET /health — health check endpoint
- Zero external dependencies (stdlib only)
- Docker-based build via goctl wrapper (golang:1.26-alpine)
- systemd unit, README with deployment docs
- Tests: broker pub/sub, slow subscriber drop, ref parsing, signature verification
- 6.0M static binary

converge-relay/scripts/test

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "${BASH_SOURCE[0]}")/.."
+./goctl go test -v ./...