feat: add Docker containerization (Dockerfile, compose, dockerignore)

Multi-stage build: frontend (Vite) + backend (TypeScript) in one container.
Production image based on node:20-alpine with health check.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,34 @@
+services:
+  tippspiel:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: wm2026-tippspiel
+    restart: unless-stopped
+    ports:
+      - "3301:3001"
+    environment:
+      - NODE_ENV=production
+      - PORT=3001
+      - DATABASE_URL=${DATABASE_URL}
+      - SUPABASE_URL=${SUPABASE_URL}
+      - SUPABASE_SERVICE_ROLE_KEY=${SUPABASE_SERVICE_ROLE_KEY}
+      - ANTHROPIC_API_KEY=${ANTHROPIC_API_KEY}
+      - FOOTBALL_API_KEY=${FOOTBALL_API_KEY}
+      - FOOTBALL_API_BASE_URL=https://api.football-data.org/v4
+      - ELEVENLABS_API_KEY=${ELEVENLABS_API_KEY}
+      - CORS_ORIGIN=${CORS_ORIGIN:-https://app.staffbase.com,http://localhost:5173}
+      - STAFFBASE_PUBLIC_KEY=${STAFFBASE_PUBLIC_KEY:-}
+      - STAFFBASE_PLUGIN_ID=${STAFFBASE_PLUGIN_ID:-}
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://localhost:3001/health"]
+      interval: 30s
+      timeout: 5s
+      start_period: 10s
+      retries: 3
+    networks:
+      - main-network
+
+networks:
+  main-network:
+    external: true