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>

install/tmpfiles-svxportal-tglist.conf

@@ -0,0 +1,5 @@
+# Canonical talkgroup list JSON, owned by the web user so the portal can save it.
+# Install:  sudo cp install/tmpfiles-svxportal-tglist.conf /etc/tmpfiles.d/svxportal-tglist.conf
+#           sudo systemd-tmpfiles --create /etc/tmpfiles.d/svxportal-tglist.conf
+# 'f' only writes the seed when the file is missing; existing data is kept.
+f /etc/svxlink/tglist.json 0664 www-data www-data - {"tgs":[],"requests":[]}