build: add .dockerignore, optimize Dockerfile for limited memory

Dockerfile

@@ -1,8 +1,8 @@
 FROM node:20-slim AS builder
-RUN apt-get update && apt-get install -y --no-install-recommends openssl ca-certificates git && rm -rf /var/lib/apt/lists/*
+RUN apt-get update && apt-get install -y --no-install-recommends openssl ca-certificates && rm -rf /var/lib/apt/lists/*
 WORKDIR /app
 COPY package.json package-lock.json* ./
-RUN npm install --no-audit --no-fund
+RUN npm cache clean --force 2>/dev/null; npm install --no-audit --no-fund --prefer-offline 2>/dev/null || npm install --no-audit --no-fund
 COPY . .
 RUN npx prisma generate --schema=./prisma/schema.prisma 2>/dev/null; exit 0
 RUN npm run build 2>/dev/null; exit 0