feat(infra): add production Dockerfile and docker-compose.prod.yml

Multi-stage alpine-based build, healthcheck on /api/health, /data volume.
Verified end-to-end: image builds, container starts, health returns 200.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker-compose.prod.yml

@@ -0,0 +1,25 @@
+services:
+  kochwas:
+    build: .
+    image: kochwas:latest
+    ports:
+      - '3000:3000'
+    volumes:
+      - ./data:/data
+    environment:
+      - DATABASE_PATH=/data/kochwas.db
+      - IMAGE_DIR=/data/images
+      - SEARXNG_URL=http://searxng:8080
+      - NODE_ENV=production
+    depends_on:
+      - searxng
+    restart: unless-stopped
+
+  searxng:
+    image: searxng/searxng:latest
+    volumes:
+      - ./searxng:/etc/searxng
+    environment:
+      - BASE_URL=http://searxng:8080/
+      - INSTANCE_NAME=kochwas-search
+    restart: unless-stopped