feat: add Docker setup for documentation site

- Dockerfile.docs for building docs container
- nginx.conf for serving static Starlight site
- docker-compose.yml updated with docs service (--profile docs)
- Updated docs installation/deployment pages

docker-compose.yml

@@ -25,5 +25,15 @@ services:
       timeout: 10s
       retries: 3
 
+  docs:
+    build:
+      context: .
+      dockerfile: Dockerfile.docs
+    ports:
+      - "4000:80"
+    restart: unless-stopped
+    profiles:
+      - docs
+
 volumes:
   deardiary_data: