feat(desktop): tray Do-Not-Disturb + Launch-on-login toggle (P6-1 web)

- useTauriDnd + manualDndAtom: the native tray "Do Not Disturb" toggle
  (lotus-dnd-changed event) OR's into the notification quiet-gate in
  ClientNonUIFeatures (both invite + message notifiers), alongside Focus Assist.
- AutostartSetting in Settings → General (desktop-only): reads/sets
  plugin:autostart via invoke. Mirrors the window-chrome setting.
- Docs: LOTUS_FEATURES desktop section (Linux parity + DND + autostart),
  LOTUS_TODO P6-1 → [~], LOTUS_BUGS verification row.

Gates: tsc/eslint/prettier clean, build OK, 661 tests. Native side committed on
cinny-desktop:main (CI-compile-pending).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/settings/general/General.tsx

@@ -102,7 +102,7 @@ import { useMessageLayoutItems } from '../../../hooks/useMessageLayout';
 import { useMessageSpacingItems } from '../../../hooks/useMessageSpacing';
 import { SequenceCardStyle } from '../styles.css';
 import { useTauriUpdater } from '../../../hooks/useTauriUpdater';
-import { isTauri as isTauriEnv } from '../../../hooks/useTauri';
+import { isTauri as isTauriEnv, invokeTauri, tauriInvoke } from '../../../hooks/useTauri';
 import { customWindowChromeAtom } from '../../../state/customWindowChrome';
 import { useDateFormatItems } from '../../../hooks/useDateFormat';
 import { playCallJoinSound } from '../../../utils/callSounds';
@@ -129,6 +129,38 @@ function DesktopChromeSetting() {
   );
 }
 
+/**
+ * P6-1 — "Launch on login" toggle (desktop only). Renders nothing in the
+ * browser. Reads the current state from the `autostart` plugin on mount and
+ * enables/disables it via the plugin commands when flipped. Not backed by an
+ * atom — the OS registration is the source of truth, mirrored into local state.
+ */
+function AutostartSetting() {
+  const [enabled, setEnabled] = useState(false);
+
+  useEffect(() => {
+    tauriInvoke()?.('plugin:autostart|is_enabled')
+      .then((value) => setEnabled(value === true))
+      .catch(() => undefined);
+  }, []);
+
+  const handleChange = (value: boolean) => {
+    invokeTauri(value ? 'plugin:autostart|enable' : 'plugin:autostart|disable');
+    setEnabled(value);
+  };
+
+  if (!isTauriEnv()) return null;
+  return (
+    <SequenceCard className={SequenceCardStyle} variant="SurfaceVariant" direction="Column">
+      <SettingTile
+        title="Launch on login"
+        description="Start Lotus Chat automatically when you sign in to your computer."
+        after={<Switch variant="Primary" value={enabled} onChange={handleChange} />}
+      />
+    </SequenceCard>
+  );
+}
+
 type ThemeSelectorProps = {
   themeNames: Record<string, string>;
   themes: Theme[];
@@ -443,6 +475,7 @@ function Appearance() {
       </SequenceCard>
 
       <DesktopChromeSetting />
+      <AutostartSetting />
 
       <SequenceCard className={SequenceCardStyle} variant="SurfaceVariant" direction="Column">
         <SettingTile