feat: migrate to typed messages, drop base64, fix AudioBuffer

- AudioBuffer getAudio(): use ab.totalBytes directly (eliminates triple-copy)
- Decode STTStreamMessage via natsutil.Decode[messages.STTStreamMessage]
- Audio chunks arrive as raw []byte (no base64 decode needed)
- Publish STTTranscription struct (not map[string]any)
- Interrupts use messages.STTInterrupt
- Remove encoding/base64 import
- Add .dockerignore, GOAMD64=v3 in Dockerfile
- All 15 tests pass

.dockerignore

@@ -0,0 +1,9 @@
+.git
+.gitignore
+*.md
+LICENSE
+renovate.json
+*_test.go
+e2e_test.go
+__pycache__
+.env*