(config) Harden Docker deployment for remote servers

Run the Django control panel with Gunicorn instead of the development
runserver and serve static files through WhiteNoise.

Add restart policies, healthchecks, .env-driven production settings, and
a sample .env file for single-server deployments. Update the Docker
entrypoint to collect static assets and document the remote server
deployment and update flow in the README.

pyproject.toml

@@ -9,6 +9,8 @@ description = "Pull-based rsync backup tool with hardlinked snapshots"
 requires-python = ">=3.11"
 dependencies = [
   "Django>=5.2,<6.0",
+  "gunicorn>=23.0,<24.0",
+  "whitenoise>=6.9,<7.0",
   "PyYAML>=6.0"
 ]