Initial import: nasmon health monitor, split out of home_nas

Go service (nasmon/) plus nfpm packaging (packaging/), carried over from
the home_nas monorepo. Adds rpm packaging alongside the existing deb
build (Fedora/RHEL/Rocky dependency names via nfpm overrides, per-format
systemd unit path, dpkg+rpm-compatible maintainer scripts) and a Gitea
Actions workflow that builds both formats on every push.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packaging/postinst.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+set -e
+# config holds the SMTP password: root only
+chmod 0600 /etc/nasmon/config.json 2>/dev/null || true
+chmod 0750 /var/lib/nasmon
+if [ -d /run/systemd/system ]; then
+  systemctl daemon-reload
+  systemctl enable nasmon.service >/dev/null 2>&1 || true
+  # restart on upgrade, start on fresh install
+  systemctl restart nasmon.service || true
+  # Windows network discovery, only when the wsdd package is present
+  if [ -x /usr/bin/wsdd ]; then
+    systemctl enable --now wsdd.service >/dev/null 2>&1 || true
+  fi
+fi
+exit 0