Public web-only release: SvxPortal front-end + auth backend, install templates and INSTALL.md

Stripped from the internal repo: per-box deploy trees, Go services (nodelist/astmeta/proxy/svxdr),
deploy/sync scripts and all secrets. Config templates for nginx, PHP-FPM, Redis and tmpfiles
live in install/ with CHANGEME placeholders.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

auth/lib/shell.php

@@ -0,0 +1,7 @@
+<?php
+declare(strict_types=1);
+// shell.php — shared PHP helper for every web (dmr-web, svx-web, svxlink-web).
+// Canonical copy: callmgr2/www-mumien/auth/lib/shell.php; other repos carry a COPY.
+
+// Shell-argument quoting for the few pages that run local helpers.
+function sh_arg($v): string { return escapeshellarg((string)$v); }