feat: rewrite pipeline-bridge in Go

Replace Python implementation with Go for smaller container images.
Uses handler-base Go module for NATS, health, and telemetry.

- main.go: pipeline bridge with Argo/Kubeflow HTTP submission
- main_test.go: 8 tests covering helpers and HTTP submit functions
- Dockerfile: multi-stage golang:1.25-alpine → scratch
- CI: Gitea Actions with lint/test/release/docker/notify

.gitignore

@@ -9,3 +9,4 @@ dist/
 build/
 .env
 .env.local
+pipeline-bridge