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/_meta.json

@@ -64,6 +64,11 @@
         "label": "Configuration Reference",
         "name": "/reference/config"
     },
+    {
+        "type": "file",
+        "label": "Environment Variables",
+        "name": "/reference/environment-variables"
+    },
     {
         "type": "dir",
         "label": "Admin Command Reference",