feat: rewrite voice-assistant in Go

Replace Python voice assistant with Go for smaller container images.
Uses handler-base Go module for NATS, health, telemetry, and all service clients.

- Full pipeline: STT → embed → Milvus → rerank → LLM → TTS
- Base64 audio encode/decode
- Dockerfile: multi-stage golang:1.25-alpine → scratch
- CI: Gitea Actions with lint/test/release/docker/notify

.gitignore

@@ -41,3 +41,4 @@ ENV/
 .env
 .env.local
 *.log
+voice-assistant