Make web port configurable via WEB_PORT environment variable

- Allows deployment when port 8000 is already in use (e.g., by Portainer)
- Defaults to 8000 if WEB_PORT not specified
- Use WEB_PORT=8001 (or any other port) to override

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docker-compose.yml

@@ -61,7 +61,7 @@ services:
       - ./media:/app/media
       - static_files:/app/staticfiles
     ports:
-      - "8000:8000"
+      - "${WEB_PORT:-8000}:8000"
     networks:
       - frontend
       - backend