Enhance environment variable documentation and configuration

- Updated `.env.example` to include new environment variables for server access logging and security settings, ensuring comprehensive configuration options.
- Revised `docker-entrypoint.sh` to clarify the source of supported environment variables.
- Improved `README.md` to reflect the latest environment variable changes and maintain synchronization with the canonical list in `internal/config/config.go`.
- Added tests to ensure documentation consistency across `.env.example` and `README.md`, preventing future discrepancies.

docker-entrypoint.sh

@@ -1,6 +1,10 @@
 #!/bin/sh
 set -eu
 
+# This script forces certain SCRATCHBOX_* vars for Docker.
+# The full list of supported env vars (single source of truth) is in
+# internal/config/config.go:envSuffixes . Update that list + docs when changing env support.
+
 # Container-enforced data directory.
 SCRATCHBOX_STORAGE_DATA_DIR=/data
 export SCRATCHBOX_STORAGE_DATA_DIR