Portability: sysfs-only sensors with thermal-zone fallback, /sys/block disk discovery, fs blacklist, pwrstat/NUT/apcupsd UPS, login shell from passwd, templated unit + install for any user, cross-compile targets

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

cmd/hamlab/main.go

@@ -12,6 +12,7 @@ import (
 	"os/signal"
 	"os/user"
 	"path/filepath"
+	"strings"
 	"syscall"
 	"time"
 
@@ -116,7 +117,7 @@ func serve(cfg *config.Config) error {
 	}
 	shell := os.Getenv("SHELL")
 	if shell == "" {
-		shell = "/bin/bash"
+		shell = loginShell(u.Username)
 	}
 	mgr := hterm.NewManager(shell, u.HomeDir)
 	mgr.OnChange = func(list []hterm.Info) {
@@ -162,3 +163,24 @@ func serve(cfg *config.Config) error {
 	}
 	return nil
 }
+
+// loginShell returns the user's shell from /etc/passwd, falling back to bash if
+// present and /bin/sh otherwise. Systemd units don't export $SHELL.
+func loginShell(username string) string {
+	if b, err := os.ReadFile("/etc/passwd"); err == nil {
+		for _, line := range strings.Split(string(b), "\n") {
+			f := strings.Split(line, ":")
+			if len(f) >= 7 && f[0] == username && f[6] != "" {
+				if _, err := os.Stat(f[6]); err == nil {
+					return f[6]
+				}
+			}
+		}
+	}
+	for _, sh := range []string{"/bin/bash", "/usr/bin/bash", "/bin/zsh", "/bin/sh"} {
+		if _, err := os.Stat(sh); err == nil {
+			return sh
+		}
+	}
+	return "/bin/sh"
+}