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/config.json

@@ -0,0 +1,32 @@
+{
+  "smtp": {
+    "host": "",
+    "port": 587,
+    "security": "starttls",
+    "user": "",
+    "pass": "",
+    "from": "",
+    "to": [],
+    "subject_prefix": "[nasmon]"
+  },
+  "alerts_enabled": true,
+  "notify_resolved": true,
+  "remind_hours": 24,
+  "smart_interval_min": 30,
+  "smart_skip_standby": true,
+  "thresholds": {
+    "disk_temp_c": 50,
+    "cpu_temp_c": 80,
+    "pool_capacity_pct": 85,
+    "scrub_max_age_days": 45,
+    "rootfs_free_pct": 10,
+    "nvme_used_pct": 90,
+    "nvme_spare_pct": 10
+  },
+  "self_tests": {
+    "enabled": false,
+    "short_days": 7,
+    "long_days": 30,
+    "hour": 3
+  }
+}