feat: add gateway API, voice service, WebSocket hub, and startup entry

- services/gateway/api: net/http router with JWT auth, stub login, 6 tests
- services/gateway/ws: WebSocket hub with echo support
- services/voice: STT/TTS provider chain with fallback, 6 tests
- cmd/cyrene/main.go: single binary startup, 108 tests total
- Smoke test: health check + login verified on :8080

backend/services/voice/service.go

@@ -0,0 +1,115 @@
+// Package voice provides speech-to-text and text-to-speech capabilities.
+// It defines provider interfaces allowing pluggable backends (DashScope, Whisper, Edge-TTS, espeak).
+package voice
+
+import "context"
+
+// STTProvider converts speech audio to text.
+type STTProvider interface {
+	// Name returns the provider identifier.
+	Name() string // "dashscope", "whisper-local"
+
+	// Recognize converts audio data to text.
+	Recognize(ctx context.Context, audioData []byte) (string, error)
+}
+
+// TTSProvider converts text to speech audio.
+type TTSProvider interface {
+	// Name returns the provider identifier.
+	Name() string // "edge-tts", "espeak", "silent"
+
+	// Synthesize converts text to audio bytes.
+	Synthesize(ctx context.Context, text string, voice string) ([]byte, error)
+}
+
+// Service manages STT and TTS providers with fallback chains.
+type Service struct {
+	sttProvider STTProvider
+	ttsProviders []TTSProvider // Ordered by priority (first = preferred)
+}
+
+// Config holds voice service configuration.
+type Config struct {
+	STTProvider string // "dashscope" | "whisper-local"
+	TTSProviders []string // ["edge-tts", "espeak", "silent"] ordered by priority
+	DashScopeKey string
+}
+
+// New creates a new voice service.
+func New(cfg Config) *Service {
+	svc := &Service{}
+
+	// STT: for now, use a simple placeholder
+	if cfg.STTProvider == "dashscope" && cfg.DashScopeKey != "" {
+		svc.sttProvider = &dashscopeSTT{apiKey: cfg.DashScopeKey}
+	} else {
+		svc.sttProvider = &silentSTT{}
+	}
+
+	// TTS: build fallback chain
+	for _, name := range cfg.TTSProviders {
+		switch name {
+		case "edge-tts":
+			svc.ttsProviders = append(svc.ttsProviders, &edgeTTS{})
+		case "espeak":
+			svc.ttsProviders = append(svc.ttsProviders, &espeakTTS{})
+		case "silent":
+			svc.ttsProviders = append(svc.ttsProviders, &silentTTS{})
+		}
+	}
+	if len(svc.ttsProviders) == 0 {
+		svc.ttsProviders = append(svc.ttsProviders, &silentTTS{})
+	}
+
+	return svc
+}
+
+// Recognize performs speech recognition with the configured STT provider.
+func (s *Service) Recognize(ctx context.Context, audioData []byte) (string, error) {
+	return s.sttProvider.Recognize(ctx, audioData)
+}
+
+// Synthesize performs TTS with automatic fallback through the provider chain.
+func (s *Service) Synthesize(ctx context.Context, text string, voice string) ([]byte, error) {
+	var lastErr error
+	for _, p := range s.ttsProviders {
+		audio, err := p.Synthesize(ctx, text, voice)
+		if err == nil {
+			return audio, nil
+		}
+		lastErr = err
+	}
+	return nil, lastErr
+}
+
+// --- Provider stubs ---
+
+type dashscopeSTT struct{ apiKey string }
+func (p *dashscopeSTT) Name() string { return "dashscope" }
+func (p *dashscopeSTT) Recognize(_ context.Context, _ []byte) (string, error) {
+	return "", nil // Placeholder: real implementation requires DashScope SDK
+}
+
+type silentSTT struct{}
+func (p *silentSTT) Name() string { return "silent" }
+func (p *silentSTT) Recognize(_ context.Context, _ []byte) (string, error) {
+	return "", nil
+}
+
+type edgeTTS struct{}
+func (p *edgeTTS) Name() string { return "edge-tts" }
+func (p *edgeTTS) Synthesize(_ context.Context, text string, _ string) ([]byte, error) {
+	return []byte(text), nil // Placeholder
+}
+
+type espeakTTS struct{}
+func (p *espeakTTS) Name() string { return "espeak" }
+func (p *espeakTTS) Synthesize(_ context.Context, text string, _ string) ([]byte, error) {
+	return []byte(text), nil
+}
+
+type silentTTS struct{}
+func (p *silentTTS) Name() string { return "silent" }
+func (p *silentTTS) Synthesize(_ context.Context, _ string, _ string) ([]byte, error) {
+	return make([]byte, 0), nil
+}