[FEATURE] Add In-App Plugin Update Notifications to AKS Desktop

## Feature Summary

Add an in-app notification experience to AKS desktop that informs users when updates are available for installed plugins. The feature should proactively notify users when a newer plugin version is available and provide a simple path to review and install the update.

## Motivation

AKS desktop is increasingly extending functionality through plugins. As new plugin versions are released, users may be unaware that updates containing bug fixes, security improvements, performance enhancements, or new capabilities are available.

Download data may suggest that many users continue running older plugin versions long after newer versions have been released. As a result, users may miss important improvements and may encounter issues that have already been addressed in later releases.

Today, users must manually visit the plugin catalog and check whether updates are available. A proactive notification experience would improve discoverability of plugin updates and help users stay current.

## Detailed Description

mplement a plugin update notification mechanism within AKS desktop that periodically checks whether newer versions of installed plugins are available.

When updates are detected:

- Display an in-app notification indicating that plugin updates are available.
- Identify which installed plugins have newer versions.
- Show the currently installed version and latest available version.
- Provide a clear action to review or install available updates.
- Allow users to dismiss the notification and continue working.
- Ensure notifications are informative but do not interrupt critical workflows.

The experience should be consistent with the existing application update notification model while being tailored specifically for plugin management.

## Alternatives Considered

### Manual Plugin Updates

Continue requiring users to periodically visit the plugin catalog and manually check for updates. This approach creates friction and relies on users remembering to check for newer versions.

### Release Notes and Announcements

Rely on release notes, documentation updates, blog posts, or community announcements to communicate plugin updates. While useful, these channels do not guarantee that users become aware of updates relevant to the plugins they have already installed.

### Automatic Plugin Updates

Plugins could automatically update in the background. While convenient, automatic updates introduce additional considerations around user control, validation, compatibility, and enterprise environments. This proposal focuses only on notifying users that updates are available.

## Use Cases

1. As an AKS Desktop user, I want to know when updates are available for my installed plugins so I can benefit from the latest fixes and capabilities.
2. When a plugin I use frequently receives a new release, I need a notification so that I do not have to manually check the plugin catalog.
3. As an administrator evaluating new capabilities, I want visibility into available plugin updates so I can determine whether they should be adopted.
4. When a plugin update contains important fixes, I need to be notified so that I can upgrade to a supported version.

## Implementation Ideas

- Periodically compare installed plugin versions against versions available in the plugin catalog.
- Check for plugin updates at application startup and at regular intervals.
- Display a toast, banner, or notification indicating available updates.
- Provide a direct action that opens the plugin catalog filtered to plugins with available updates.
- Surface the number of available plugin updates within the plugin catalog UI.
- Capture telemetry on update discovery, notification visibility, and update adoption rates.

## Additional Context

Unlike AKS desktop application updates, plugin updates can be released independently and more frequently. Increasing visibility of available plugin updates can help ensure users receive improvements and fixes without relying on external communications or manual catalog checks.

This proposal is focused on update awareness and discovery. Automatic plugin installation or background updates are out of scope.

## Acceptance Criteria

- [ ] AKS desktop can determine when updates are available for installed plugins.
- [ ] Users receive an in-app notification when one or more plugin updates are available.
- [ ] Notifications identify which plugins have updates available.
- [ ] Notifications include installed and available versions.
- [ ] Users can dismiss the notification without disrupting their workflow.
- [ ] Users are provided a direct path to review and update affected plugins.
- [ ] No notification is displayed when installed plugins are already up to date.
- [ ] The experience is consistent with other update notification experiences within AKS desktop.

## Checklist

- [ ] I have searched for existing feature requests
- [ ] I have provided clear use cases
- [ ] I have considered alternatives
- [ ] This feature aligns with the project's goals