Portable install: the binary installs itself; static builds on five architectures; root via sudo, doas or uid 0; every package manager; older systemd; no lsblk

- hamlab install / uninstall (internal/setup): systemd or OpenRC, elevates through
  sudo or doas, runs as the invoking user, sets or generates the password, names only
  journal groups that exist, waits for /healthz, reports an active firewalld/ufw.
  --purge and the data chown never touch a directory that isn't Ham Lab's alone.
- install.sh: curl-able bootstrap (arch detection, SHA256SUMS, offline beside the
  binaries, noexec /tmp fallback). make release builds dist/ for amd64, arm64, arm
  (ARMv6), 386, riscv64. Every build is CGO_ENABLED=0; the native one used to link glibc.
- internal/priv replaces every literal `sudo -n`: uid 0, sudo or doas.
- Updates acts on dnf, zypper, pacman and apk as well as apt; dnf shows installed versions.
- Services falls back to the plain systemctl table before systemd 246 and says so on
  hosts without systemd. Disks falls back to /sys/block without lsblk.
- Listener binds with IP_FREEBIND, so a LAN address that isn't up at boot is no failure.
- Self-update: the new build must pass `check` against the live config, is put in
  place by atomic rename, and the daemon re-execs itself (same under any supervisor).
- State and config writes are fsynced; a corrupt state.json is set aside, not fatal.
- Terminal shutdown no longer empties the saved list, so names come back after a
  restart by design rather than by winning a race.
- Config default is ~/.config/hamlab; an existing ~/apps/hamlab is still found.

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

internal/config/config.go

@@ -9,6 +9,8 @@ import (
 	"path/filepath"
 	"sync"
 	"time"
+
+	"hamlab/internal/store"
 )
 
 // Token is an API token another Ham Lab (a hub) uses to manage this host. Only the
@@ -40,6 +42,25 @@ type Config struct {
 	mu   sync.Mutex
 }
 
+// Candidates lists where config.json may live under a home directory, preferred first:
+// the XDG location, then ~/apps/hamlab, which installs before v0.2 used.
+func Candidates(home string) []string {
+	return []string{filepath.Join(home, ".config", "hamlab", "config.json"), filepath.Join(home, "apps", "hamlab", "config.json")}
+}
+
+// DefaultPath is the config used when neither -config nor $HAMLAB_CONFIG says otherwise:
+// whichever candidate exists, else the preferred one.
+func DefaultPath() string {
+	home, _ := os.UserHomeDir()
+	c := Candidates(home)
+	for _, p := range c {
+		if _, err := os.Stat(p); err == nil {
+			return p
+		}
+	}
+	return c[0]
+}
+
 func Default(path string) *Config {
 	return &Config{Listen: "127.0.0.1:8100", path: path}
 }
@@ -77,11 +98,7 @@ func (c *Config) save() error {
 	if err != nil {
 		return err
 	}
-	tmp := c.path + ".tmp"
-	if err := os.WriteFile(tmp, append(b, '\n'), 0o600); err != nil {
-		return err
-	}
-	return os.Rename(tmp, c.path)
+	return store.WriteFileAtomic(c.path, append(b, '\n'), 0o600)
 }
 
 // Update applies fn under the lock and saves.