修复Docker构建：修正embed路径为cmd/embedded/dist

Dockerfile

@@ -24,9 +24,9 @@ RUN go mod download
 
 COPY backend/ ./
 
-RUN mkdir -p embedded/dist
+RUN mkdir -p cmd/embedded/dist
 
-COPY --from=frontend-builder /app/frontend/dist ./embedded/dist/
+COPY --from=frontend-builder /app/frontend/dist ./cmd/embedded/dist/
 
 RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o main ./cmd/main.go