Initial commit: Daily tech newsletter worker

A Node.js/TypeScript worker that sends daily AI-generated summaries
of tech news from X/Twitter via Nitter RSS feeds.

Features:
- Fetches tweets from 40+ curated tech accounts via Nitter RSS
- Filters and categorizes by topic (AI/ML, SWE, General Tech)
- Generates AI summaries using OpenRouter (Claude/GPT-4)
- Sends professional HTML email via Brevo SMTP
- Runs on cron schedule inside Docker container
- Instance rotation for Nitter reliability
- Graceful degradation if AI fails

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker/Dockerfile

@@ -0,0 +1,42 @@
+# =============================================================================
+# Build Stage
+# =============================================================================
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+
+# Install dependencies first (better layer caching)
+COPY package*.json ./
+RUN npm ci
+
+# Copy source and build
+COPY tsconfig.json ./
+COPY src ./src
+RUN npm run build
+
+# Prune dev dependencies
+RUN npm prune --production
+
+# =============================================================================
+# Production Stage
+# =============================================================================
+FROM node:20-alpine AS production
+
+# Security: run as non-root user
+RUN addgroup -g 1001 -S nodejs && \
+    adduser -S newsletter -u 1001
+
+WORKDIR /app
+
+# Copy built application
+COPY --from=builder --chown=newsletter:nodejs /app/node_modules ./node_modules
+COPY --from=builder --chown=newsletter:nodejs /app/dist ./dist
+COPY --from=builder --chown=newsletter:nodejs /app/package.json ./
+
+USER newsletter
+
+# Set timezone (can be overridden via env)
+ENV TZ=Europe/Warsaw
+
+# Default command
+CMD ["node", "dist/index.js"]