feat: Phase 5 STT — DashScope Gummy 实时语音识别 + 本地 Whisper 回退

- DashScope WebSocket STT 客户端 (gummy-chat-v1)
- 双引擎架构: DashScope 优先, Whisper 本地回退
- 实时流式 STT WebSocket 端点
- DevTools 模型搜索框焦点修复

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/voice-service/go.mod

@@ -4,4 +4,7 @@ go 1.26.2
 
 replace github.com/yourname/cyrene-ai/pkg/logger => ../pkg/logger
 
-require github.com/yourname/cyrene-ai/pkg/logger v0.0.0
+require (
+	github.com/gorilla/websocket v1.5.3
+	github.com/yourname/cyrene-ai/pkg/logger v0.0.0
+)