Linux x86_64 offline release; configurable API and bundled PostgreSQL ports.

- packaging/linux: netx-<ver>-linux-x86_64.tar.gz with bundled Python 3.12,
  PostgreSQL 16 and web/dist (glibc >= 2.17). install.sh (install/update/
  reinstall), netxctl (start/stop/status/logs, set-port, set-bind,
  set-pg-port, reconfigure-db, check-update/update/auto-update, backup,
  uninstall), systemd units, nohup fallback without systemd. Privilege
  drop, detaching and tar go through the bundled Python, so bare images
  without su/runuser/setsid/tar work.
- Updates: same GitHub/Forgejo/manifest sources as Windows, sha256
  verified, pre-update pg_dump, automatic rollback when the new version
  does not come up.
- Non-loopback bind: generated bootstrap admin password and
  NETX_UME_VERIFY_TLS=true, as security_bootstrap requires.
- Build in manylinux2014 + check_bundle.sh (GLIBC <= 2.17, no missing
  libs); release-linux.yml builds on v* tags and smoke-tests offline on
  CentOS 7, Rocky 9, Ubuntu 18.04/24.04, Debian 12, openSUSE Leap 15 and
  openEuler 22.03 before attaching to the release.
- Windows: Setup DB page gets a bundled PG port field and
  /BundledPgPort=; set_pg_port.ps1 + tray "Built-in database port";
  reconfigure keeps the configured port; postgresql.conf is written
  without a BOM (PS 5.1 Set-Content -Encoding utf8 broke postgres).
- Forgejo/GitHub publish scripts include the Linux package.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/README.md

@@ -1,6 +1,6 @@
 # NetX Windows packaging
 
-**Linux is unchanged:** keep using your own PostgreSQL and `NETX_DATABASE_URL` with `scripts/start_netx.sh`. Nothing under this folder is required on Linux.
+**Linux:** the offline `netx-<ver>-linux-x86_64.tar.gz` package lives in [`linux/`](linux/README.md) (install.sh + netxctl). `scripts/start_netx.sh` stays for running from a source checkout.
 
 This directory builds a Windows deliverable with: