docs: add example.env and document all environment variables

- Create example.env with all 31 environment variables documented
- Update docker-compose.yml to use env_file directive
- Update doc/deployment.md with Quick Start and missing variables
- Add OXICLOUD_BASE_URL and WOPI configuration docs
- Update README.md Docker section with .env setup
- Remove duplicate port mapping (incorporates 4577e56)
- Fix server port default from 8085 to 8086

docker-compose.yml

@@ -27,15 +27,13 @@ services:
       dockerfile: Dockerfile
     ports:
       - "8086:8086"
-      - "8085:8085"
     networks:
       - oxicloud
     depends_on:
       postgres:
         condition: service_healthy
-    environment:
-      - "OXICLOUD_DB_CONNECTION_STRING=postgres://postgres:postgres@postgres/oxicloud"
-      - "DATABASE_URL=postgres://postgres:postgres@postgres/oxicloud"
+    env_file:
+      - .env
     volumes:
       - storage_data:/app/storage
       - ./static:/app/static