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/internal/config/config.go

@@ -9,6 +9,10 @@ type Config struct {
 	WhisperModel    string
 	WhisperLanguage string
 	MaxAudioSize    int64 // 字节
+
+	// DashScope STT 配置
+	DashScopeAPIKey string
+	DashScopeModel  string
 }
 
 // Load 从环境变量加载配置
@@ -19,6 +23,8 @@ func Load() *Config {
 		WhisperModel:    getEnv("WHISPER_MODEL", "./whisper.cpp/models/ggml-small.bin"),
 		WhisperLanguage: getEnv("WHISPER_LANGUAGE", "zh"),
 		MaxAudioSize:    10 * 1024 * 1024, // 10MB
+		DashScopeAPIKey: getEnv("DASHSCOPE_API_KEY", ""),
+		DashScopeModel:  getEnv("DASHSCOPE_STT_MODEL", "gummy-chat-v1"),
 	}
 }