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)

client/src/components/settings/AutostartSettings.tsx

@@ -0,0 +1,58 @@
+/**
+ * @file AutostartSettings — Settings → About's "Start automatically" switch:
+ * whether the dashboard starts at boot/login through the per-user service
+ * (systemd `--user` unit, or a LaunchAgent on macOS), over
+ * `GET/PUT /api/settings/autostart`. Off by default; a change never starts or
+ * stops the running server.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { useEffect, useState } from "react";
+import { useTranslation } from "react-i18next";
+import { api, type AutostartStatus } from "../../lib/api";
+import { toast } from "../../lib/toast";
+import { SettingsSection, SettingsSwitchRow } from "./SettingsRow";
+
+export function AutostartSettings() {
+  const { t } = useTranslation("settings");
+  const [status, setStatus] = useState<AutostartStatus | null>(null);
+  const [saving, setSaving] = useState(false);
+
+  useEffect(() => {
+    api.settings.autostart
+      .get()
+      .then(setStatus)
+      .catch(() => {});
+  }, []);
+
+  const change = async (enabled: boolean) => {
+    setSaving(true);
+    try {
+      setStatus(await api.settings.autostart.set(enabled));
+    } catch (err) {
+      toast.error(err instanceof Error ? err.message : String(err));
+    } finally {
+      setSaving(false);
+    }
+  };
+
+  const note = !status
+    ? undefined
+    : !status.available
+      ? t("autostart.unavailable")
+      : status.foreign
+        ? t("autostart.foreign")
+        : t(`autostart.desc_${status.kind}`);
+
+  return (
+    <SettingsSection id="autostart" title={t("autostart.title")}>
+      <SettingsSwitchRow
+        label={t("autostart.label")}
+        description={note}
+        checked={!!status?.enabled}
+        disabled={!status?.available || status.foreign || saving}
+        onChange={(v) => void change(v)}
+      />
+    </SettingsSection>
+  );
+}