fix: preserve notification plugin listener context

The notification plugin can return an object whose unregister method
expects its original listener object as this. Calling the extracted
method directly drops that context and produces an unhandled rejection
when the browser shell cleans up listeners.

Constraint: The desktop frontend also runs in browser-like dev shells where Tauri plugin APIs may be partially present
Rejected: Ignore cleanup errors | it leaves noisy unhandled rejections during local UI smoke tests
Confidence: high
Scope-risk: narrow
Tested: cd desktop && bun run test -- desktopNotifications
Not-tested: Native notification click behavior on every desktop platform

desktop/src/lib/desktopNotifications.test.ts

@@ -344,7 +344,11 @@ describe('desktopNotifications', () => {
 
   it('forwards notification click targets from native and plugin listeners', async () => {
     const unlistenNative = vi.fn()
-    const unregisterPlugin = vi.fn()
+    const pluginListener = {
+      unregister: vi.fn(function (this: unknown) {
+        expect(this).toBe(pluginListener)
+      }),
+    }
     type NativeClickCallback = (event: { payload: unknown }) => void
     type PluginClickCallback = (notification: unknown) => void
     let nativeCallback: NativeClickCallback = () => {
@@ -366,7 +370,7 @@ describe('desktopNotifications', () => {
     notificationPluginMock.onAction.mockImplementation(async (callback: (notification: unknown) => void) => {
       pluginCallback = callback
       pluginRegistered = true
-      return { unregister: unregisterPlugin }
+      return pluginListener
     })
 
     const onTarget = vi.fn()
@@ -382,7 +386,7 @@ describe('desktopNotifications', () => {
 
     cleanup()
     expect(unlistenNative).toHaveBeenCalledTimes(1)
-    expect(unregisterPlugin).toHaveBeenCalledTimes(1)
+    expect(pluginListener.unregister).toHaveBeenCalledTimes(1)
   })
 
   it('requests OS-level window attention for blocking prompts', async () => {

desktop/src/lib/desktopNotifications.ts

@@ -339,7 +339,7 @@ function disposePluginListener(listener: unknown): void {
   const unregister = listener && typeof listener === 'object'
     ? (listener as { unregister?: () => Promise<void> | void }).unregister
     : undefined
-  if (unregister) void unregister()
+  if (typeof unregister === 'function') void unregister.call(listener)
 }
 
 export async function installDesktopNotificationClickListener(