feat: start-at-login is a Settings switch, off by default (v2.5.0)

- Settings → About → "Start AgentHub automatically" (AutostartSettings.tsx,
  GET/PUT /api/settings/autostart, server/lib/autostart.js). The switch is
  the systemd --user unit's / LaunchAgent's enabled state: on writes a unit
  for the running server when none exists and enables it, off disables it;
  neither starts or stops the server. A foreign unit is never touched
  (409 EFOREIGN)
- The plugin bootstrap no longer installs a unit on every install: it
  installs or starts one only while the user has it enabled, and a rewrite
  keeps the enabled state (writeUserService({ enable })). An install that
  already had the unit enabled stays on. A stale-but-enabled unit beside a
  live detached server is repointed, no longer started onto the bound port
- unitIsEnabled / setUnitEnabled in systemd-service.js and launchd-service.js

Also:
- fix(workspace): status bar no longer covers the chat box below md (#61)

server/lib/autostart.js

@@ -0,0 +1,79 @@
+/**
+ * @file autostart.js
+ * @description Settings → About's "Start automatically" switch: whether the
+ * dashboard starts at boot/login through the per-user service
+ * (`scripts/service-manager.js` — a systemd `--user` unit, or a LaunchAgent on
+ * macOS). The switch IS the unit's enabled state, nothing stored beside it.
+ * Turning it on writes a unit for THIS server when none exists, and enables
+ * it; turning it off disables it. Neither ever starts or stops anything — the
+ * server answering the click is the one that would die. Off by default: the
+ * plugin bootstrap installs no unit until the user opts in.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+const fs = require("fs");
+const path = require("path");
+const svc = require("../../scripts/service-manager");
+
+const NAME = "agenthub";
+const ROOT = path.resolve(__dirname, "..", "..");
+
+/** A unit by our name that AgentHub did not write — never ours to touch. */
+function isForeign() {
+  return fs.existsSync(svc.unitPath(NAME)) && !svc.unitIsOurs(NAME);
+}
+
+function status() {
+  const available = svc.systemctlAvailable();
+  return {
+    available,
+    kind: svc.kind,
+    enabled: available && svc.unitIsEnabled(NAME),
+    foreign: isForeign(),
+  };
+}
+
+/** The unit for the running server — same shape the bootstrap writes. */
+function unitForThisServer() {
+  const entry = path.join(ROOT, "server", "index.js");
+  const env = { NODE_ENV: "production", PATH: process.env.PATH || "" };
+  for (const key of ["NODE_PATH", "DASHBOARD_CLIENT_DIST", "DASHBOARD_PORT"]) {
+    if (process.env[key]) env[key] = process.env[key];
+  }
+  return {
+    name: NAME,
+    description: "AgentHub dashboard server",
+    workingDir: ROOT,
+    execStart: `${process.execPath} ${entry}`,
+    argv: [process.execPath, entry],
+    env,
+  };
+}
+
+function fail(code, message) {
+  return Object.assign(new Error(message), { code });
+}
+
+function setEnabled(on) {
+  if (!svc.systemctlAvailable()) {
+    throw fail("EUNAVAILABLE", `no ${svc.label} manager is available on this machine`);
+  }
+  let result;
+  if (svc.unitIsOurs(NAME)) result = svc.setUnitEnabled(NAME, on);
+  else if (isForeign()) result = "foreign";
+  else if (!on)
+    result = "ok"; // nothing installed: already off
+  else {
+    result = svc.writeUserService(unitForThisServer()); // writes + enables, starts nothing
+    if (result === "written") svc.enableLinger();
+  }
+  if (result === "foreign") {
+    throw fail("EFOREIGN", `${svc.unitPath(NAME)} was not written by AgentHub — not touching it`);
+  }
+  if (result === "failed" || result === "unavailable") {
+    throw fail("ESERVICE", `could not change the ${svc.label}`);
+  }
+  return status();
+}
+
+module.exports = { status, setEnabled };