Initial MVP: DocFast PDF API

- HTML/Markdown to PDF conversion via Puppeteer
- Invoice and receipt templates
- API key auth + rate limiting
- Dockerfile for deployment

Dockerfile

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+FROM node:22-slim
+
+# Chrome deps
+RUN apt-get update && apt-get install -y --no-install-recommends \
+  libatk1.0-0t64 libatk-bridge2.0-0t64 libcups2t64 libdrm2 \
+  libxkbcommon0 libxcomposite1 libxdamage1 libxfixes3 libxrandr2 \
+  libgbm1 libpango-1.0-0 libpangocairo-1.0-0 libcairo2 \
+  libasound2t64 libnspr4 libnss3 fonts-liberation \
+  && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+COPY package*.json ./
+RUN npm ci --omit=dev
+COPY dist/ dist/
+
+ENV PORT=3100
+EXPOSE 3100
+USER node
+CMD ["node", "dist/index.js"]