feat: rewrite stt-module (HTTP variant) in Go

Replace Python streaming STT service with Go for smaller container images.
Local Whisper/ROCm variant (stt_streaming_local.py, Dockerfile.rocm) stays Python.

- AudioBuffer with session state management (listening/responding)
- RMS-based voice activity detection (pure Go, no cgo)
- Interrupt detection during LLM response playback
- JetStream AI_VOICE_STREAM setup
- Session auto-creation and cleanup
- 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
+stt-module