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/collect/exec.go

@@ -0,0 +1,28 @@
+package collect
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"os/exec"
+	"time"
+)
+
+// run executes a command with a timeout and returns stdout even on non-zero
+// exit (smartctl encodes state in its exit code and still prints JSON).
+func run(timeout time.Duration, name string, args ...string) ([]byte, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+	cmd := exec.CommandContext(ctx, name, args...)
+	var out, errb bytes.Buffer
+	cmd.Stdout, cmd.Stderr = &out, &errb
+	err := cmd.Run()
+	if err != nil {
+		var ee *exec.ExitError
+		if errors.As(err, &ee) {
+			return out.Bytes(), ee
+		}
+		return out.Bytes(), errors.New(name + ": " + err.Error() + " " + errb.String())
+	}
+	return out.Bytes(), nil
+}