fix: add libc6-compat to builder stage for SWC binary

The Next.js SWC binary requires libc6-compat on Alpine Linux.
It was only installed in the deps stage but not the builder stage,
causing build failures on fresh (no-cache) Docker builds.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/mobile-upgrade/Dockerfile

@@ -11,6 +11,7 @@ RUN npm ci --only=production=false
 
 # 阶段2: 构建
 FROM node:20-alpine AS builder
+RUN apk add --no-cache libc6-compat
 WORKDIR /app
 
 # 复制依赖