[ENHANCEMENT] Add or improve visibility of manual update *check* feature

### Please confirm these before moving forward

- [X] I have searched for my feature proposal and not found a work-in-progress/duplicate/resolved/discarded issue.
- [X] This improvements refers to an existing feature. If you want to suggest a new feature, please use [this template](https://github.com/marticliment/WingetUI/issues/new?assignees=marticliment&labels=new-feature&projects=&template=feature-request.yml&title=%5BFEATURE+REQUEST%5D+%28Enter+your+description+here%29)
- [X] This improvements is not a bug. If you want to report a bug, please use [this template](https://github.com/marticliment/WingetUI/issues/new?assignees=marticliment&labels=bug&projects=&template=bug-issue.yml&title=%5BBUG%5D+%28Enter+your+description+here%29)

### Describe the improvement

I would like to be able to manually request that WingetUI check for available updates.

Ideally there would be both an option on the system tray right-click menu, and a prominent button on the "Software Updates" tab of the main GUI window.

It's possible that the refresh icon next to the search box in the upper-right corner of the main GUI window does this, but:
- it has no tooltip explaining its function
- it's tiny and off in a corner of the window
- its location next to the search box suggests it has something to do with searching/filtering of the list

### Describe how this improvement could help users.

Being able to manually trigger update checks seems like a must-have feature for a package management user interface.