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>

internal/store/store_test.go

@@ -0,0 +1,48 @@
+package store
+
+import (
+	"database/sql"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+// TestMigrateOldAlertsTable opens a database created by the first release
+// (no acked_at column) and checks that the column is added.
+func TestMigrateOldAlertsTable(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "old.db")
+	db, err := sql.Open("sqlite", path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = db.Exec(`CREATE TABLE alerts (id INTEGER PRIMARY KEY, key TEXT NOT NULL, level TEXT NOT NULL, title TEXT NOT NULL,
+		detail TEXT NOT NULL, opened_at INTEGER NOT NULL, resolved_at INTEGER, last_notified_at INTEGER);
+		INSERT INTO alerts(key, level, title, detail, opened_at) VALUES('k', 'warn', 't', 'd', 1)`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	db.Close()
+
+	st, err := Open(path)
+	if err != nil {
+		t.Fatalf("open with migration: %v", err)
+	}
+	defer st.Close()
+	open, err := st.OpenAlerts()
+	if err != nil || len(open) != 1 || open[0].Acked() {
+		t.Fatalf("after migration: %+v %v", open, err)
+	}
+	if err := st.AckAlert(open[0].ID, time.Now()); err != nil {
+		t.Fatal(err)
+	}
+	act, _ := st.ActiveAlerts()
+	if len(act) != 0 {
+		t.Fatalf("acked alert listed as active")
+	}
+	// opening again must not fail (column already there)
+	st2, err := Open(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	st2.Close()
+}