Add Docker Compose deployment

- Dockerfile: Node.js 20 Alpine, single-stage build
- docker-compose.yml: backend + nginx, named volume for SQLite
- server.js: updated for Docker (env vars for PORT/DATA_DIR)
- nginx.conf: updated for Docker networking (backend hostname)
- README.md: full deployment instructions

deploy/docker-compose.yml

@@ -0,0 +1,36 @@
+services:
+  backend:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: project-tracker-api
+    restart: unless-stopped
+    volumes:
+      - project-data:/app/data
+    environment:
+      - PORT=3000
+      - NODE_ENV=production
+    networks:
+      - project-tracker-net
+
+  nginx:
+    image: nginx:alpine
+    container_name: project-tracker-nginx
+    restart: unless-stopped
+    ports:
+      - "80:80"
+    volumes:
+      - ./nginx.conf:/etc/nginx/conf.d/default.conf:ro
+      - ../frontend:/usr/share/nginx/html:ro
+    depends_on:
+      - backend
+    networks:
+      - project-tracker-net
+
+volumes:
+  project-data:
+    name: project-tracker-data
+
+networks:
+  project-tracker-net:
+    name: project-tracker-net