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/hooks/useTauriUpdater.ts

@@ -1,7 +1,7 @@
-import { useCallback } from 'react';
+import { useCallback, useEffect } from 'react';
 import { atom, useAtom, useSetAtom } from 'jotai';
 import { useTauriEvent } from './useTauri';
-import { UpdatePhase, parseUpdateError } from '../utils/updateErrors';
+import { InstallKind, UpdatePhase, parseUpdateError, toInstallKind } from '../utils/updateErrors';
 
 type TauriInternals = { invoke: (cmd: string, args?: Record<string, unknown>) => Promise<unknown> };
 const tauriInvoke = (): TauriInternals['invoke'] | undefined =>
@@ -36,6 +36,11 @@ export type UpdateFailure = { phase: UpdatePhase; message: string };
 // mid-request by the resolve/reject below, so nothing gets stuck.
 const updateStatusAtom = atom<UpdateStatus>({ state: 'idle' });
 
+// How this install gets updated; asked once. A desktop build without the
+// command (older than it) rejects the call: keep the old in-app behaviour.
+const installKindAtom = atom<InstallKind | undefined>(undefined);
+let installKindRequested = false;
+
 /**
  * Mirror native download progress into the status. Mounted once (in
  * TauriUpdateFeature) so the listener isn't duplicated per consumer.
@@ -50,6 +55,16 @@ export function useTauriUpdateProgress(): void {
 export function useTauriUpdater() {
   const isTauri = !!tauriInvoke();
   const [status, setStatus] = useAtom(updateStatusAtom);
+  const [installKind, setInstallKind] = useAtom(installKindAtom);
+
+  useEffect(() => {
+    const invoke = tauriInvoke();
+    if (!invoke || installKindRequested) return;
+    installKindRequested = true;
+    invoke('update_install_kind')
+      .then((kind) => setInstallKind(toInstallKind(kind)))
+      .catch(() => setInstallKind('in-app'));
+  }, [setInstallKind]);
 
   const check = useCallback(async () => {
     const invoke = tauriInvoke();
@@ -89,5 +104,5 @@ export function useTauriUpdater() {
     }
   }, [setStatus]);
 
-  return { isTauri, status, check, install };
+  return { isTauri, status, check, install, installKind: installKind ?? 'in-app' };
 }