refactor(docker): runner stage 复用 base 而非重新 FROM

- 将 runner stage 从 'FROM node:20-alpine' 改为 'FROM base'
- 统一版本管理，只需修改 base stage 一处
- 避免 base 和 runner 使用不同 Node 版本的风险

apps/api/Dockerfile

@@ -57,7 +57,7 @@ RUN pnpm db:generate
 # ============================================
 # Runner stage: Production image
 # ============================================
-FROM node:20-alpine AS runner
+FROM base AS runner
 WORKDIR /app
 
 ENV NODE_ENV=production

apps/web/Dockerfile

@@ -37,7 +37,7 @@ RUN pnpm build
 # ============================================
 # Runner stage: Production image
 # ============================================
-FROM node:20-alpine AS runner
+FROM base AS runner
 WORKDIR /app
 
 ENV NODE_ENV=production