feat: migrate to typed messages, drop base64

- Decode TTSRequest via natsutil.Decode[messages.TTSRequest]
- Stream audio as raw bytes via messages.TTSAudioChunk (no base64)
- Non-stream response uses messages.TTSFullResponse
- Status updates use messages.TTSStatus
- Voice list/refresh use messages.TTSVoiceListResponse/TTSVoiceRefreshResponse
- Registry returns []messages.TTSVoiceInfo (not []map[string]any)
- Remove strVal/boolVal helpers
- Add .dockerignore, GOAMD64=v3 in Dockerfile
- Update tests for typed structs (13 tests pass)

Dockerfile

@@ -14,7 +14,7 @@ RUN go mod download
 COPY . .
 
 # Build static binary
-RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o /tts-module .
+RUN CGO_ENABLED=0 GOOS=linux GOAMD64=v3 go build -ldflags="-w -s" -o /tts-module .
 
 # Runtime stage - scratch for minimal image
 FROM scratch