docs(docker): Restructure deployment guide and add env var reference

Add Quick Run section with complete getting-started workflow including
admin user creation via --execute flag. Consolidate Docker Compose to
treat reverse proxy as essential with Traefik/Caddy/nginx examples.

Move detailed image building to development guide, keeping deployment
docs focused on using pre-built images.

Create environment variables reference with practical examples and
context. Clarify built-in TLS is for testing only; production should
use reverse proxies.

docs/deploying/docker-compose.for-traefik.yml

@@ -8,7 +8,6 @@ services:
     restart: unless-stopped
     volumes:
       - db:/var/lib/continuwuity
-      - /etc/resolv.conf:/etc/resolv.conf:ro # Use the host's DNS resolver rather than Docker's.
       #- ./continuwuity.toml:/etc/continuwuity.toml
     networks:
       - proxy