fix(desktop updates): Linux package installs update via their package manager

Reported on CachyOS: "Check for Updates → The update downloaded but
couldn't be installed … Permission denied (os error 13) at path
/usr/bin/tauri_current_app…". The app was installed from the Arch package;
Tauri's Linux updater can only replace an AppImage.

With cinny-desktop's new update_install_kind command:
- pacman / deb installs: the toast says the update is available and opens
  Settings → General → App Updates, which shows the package-manager command
  (`sudo pacman -U …pkg.tar.zst`, or the .deb + `sudo apt install`) with
  Copy command and Download package — no Install & Restart that can't work.
  "Copied" only when the clipboard write actually succeeded.
- other distros: a link to the downloads page.
- Windows, AppImage, and desktop builds without the command: unchanged
  in-app update.
- a native "package-managed" refusal shows the same help.

Tests: unit (kinds, commands, refusal detection); in the real client with a
simulated desktop bridge: pacman → toast + Settings command/buttons,
install never attempted; older desktop → in-app flow as before. Unit 1321,
Playwright 26 passed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -69,6 +69,7 @@ import { dismissToastAtom, toastQueueAtom } from '../../state/toast';
 import { useReminders } from '../../hooks/useReminders';
 import { getRoomRetentionMs, isExpired } from '../../utils/retention';
 import { useTauriUpdateProgress, useTauriUpdater } from '../../hooks/useTauriUpdater';
+import { settingsRequestAtom } from '../../state/settingsRequest';
 import { isNetworkUpdateError } from '../../utils/updateErrors';
 import { invokeTauri, isTauri as isTauriApp, useTauriEvent } from '../../hooks/useTauri';
 import { CloseBehaviorPrompt } from '../../components/CloseBehaviorPrompt';
@@ -913,7 +914,8 @@ const UPDATE_PROGRESS_TOAST = 'tauri-update-progress';
 const UPDATE_FAILED_TOAST = 'tauri-update-failed';
 
 function TauriUpdateFeature() {
-  const { isTauri, status, check, install } = useTauriUpdater();
+  const { isTauri, status, check, install, installKind } = useTauriUpdater();
+  const requestSettings = useSetAtom(settingsRequestAtom);
   useTauriUpdateProgress();
   const setToast = useSetAtom(toastQueueAtom);
   const dismissToast = useSetAtom(dismissToastAtom);
@@ -972,18 +974,24 @@ function TauriUpdateFeature() {
     if (status.state !== 'available') return;
     if (firedRef.current === status.version) return;
     firedRef.current = status.version;
+    // A Linux package install can't be updated in place: point at the
+    // package-manager command in Settings instead of an install that fails.
+    const viaPackage = installKind !== 'in-app';
     setToast({
       id: `tauri-update-${status.version}`,
       displayName: '⬆ Update Available',
-      body: `Lotus Chat ${status.version} is ready. Click to install and restart.`,
+      body: viaPackage
+        ? `Lotus Chat ${status.version} is available. Click for the command to update it with your package manager.`
+        : `Lotus Chat ${status.version} is ready. Click to install and restart.`,
       roomName: 'System',
       roomId: '',
       onClick: () => {
-        installFromToast();
+        if (viaPackage) requestSettings('general');
+        else installFromToast();
       },
       sticky: true,
     });
-  }, [status, setToast, installFromToast]);
+  }, [status, setToast, installFromToast, installKind, requestSettings]);
 
   // [cinny-desktop #6] Mirror a pending update into the tray ("Restart to
   // update" + tooltip) so a dismissed toast isn't the only reminder. Kept while