refactor: trim env.example to genuinely customer-facing config only

Full review of what belongs in the public installer vs. what customers
should never need to see, per an explicit audit request:

- Removed DB_USER/DB_NAME as customer-configurable env vars entirely --
  nothing outside this compose stack ever connects to Postgres directly,
  so there was no real reason a customer would ever change these.
  Hardcoded to postgres/argus in docker-compose.yml and the two scripts
  that referenced them (backup.sh, restore.sh); DB_PASSWORD remains the
  one real secret, still auto-generated by install.sh.
- Removed ANIS_ADMIN_KEY entirely -- confirmed dead in a prior session's
  audit: it's ANIS's own admin-dashboard credential, unrelated to the
  ARGUS<->ANIS intelligence protocol, which ARGUS never sends. Carried
  over into this file by copy-paste from ANIS's own env template, not
  because ARGUS ever uses it.
- Reordered/re-commented env.example around what a customer actually
  might touch (timezone, ANIS bootstrap trio, network ports for
  conflict resolution, DOCKER_API_VERSION for NAS platforms) versus
  what's fully automated (DB_PASSWORD) -- with an explicit note that
  ongoing product configuration (WAF, DNS, users, policies) happens in
  the dashboard, not this file.
- ANIS_ENABLED/ANIS_URL defaults aligned with the Community Edition
  auto-provisioning decision (true / https://anis.weboria.eu) --
  previously still showed the pre-decision false/empty defaults since
  this repo's initial population predated that change landing.
- Flagged CHANGELOG.md as stale (last entry v3.29.0, well behind the
  current shipped version) with an honest note rather than silently
  leaving a misleading "GitHub Releases page" pointer or backfilling
  invented descriptions of past releases.

No file needed to move to the private repo -- everything here (install/
update/backup/restore/healthcheck/uninstall scripts, the compose
manifest, license/notice docs) is either required for the customer to
install and operate ARGUS or a legal-transparency requirement. None of
it is build logic, dev configuration, or reproducible source.

backup.sh

@@ -24,7 +24,7 @@ bold "Backing up ARGUS..."
 WORKDIR="$(mktemp -d)"
 trap 'rm -rf "$WORKDIR"' EXIT
 
-docker compose exec -T db pg_dump -U "${DB_USER:-postgres}" "${DB_NAME:-argus}" | gzip > "$WORKDIR/db.sql.gz"
+docker compose exec -T db pg_dump -U postgres argus | gzip > "$WORKDIR/db.sql.gz"
 ok "Database dumped"
 
 docker run --rm -v argus_api_data:/data -v "$WORKDIR":/backup alpine \