[UI]: launching on tray icon doesn't check for existing tabs or PWA

- [x] I am on the [**latest beta v0.12.3b19**](https://github.com/ActivityWatch/activitywatch/releases/tag/v0.12.3b19) ActivityWatch version.
- [x] I have searched the issues of this repo and believe that this is not a duplicate.

- **OS name and version**: Windows 10 LTSC 2021 (version 21H2) x64 EN
- **ActivityWatch version**: 0.12.3b**19**
- **Browser**: [Ungoogled Chromium 125.0.6422.113](https://github.com/macchrome/winchrome/releases/tag/v125.6422.113-M125.0.6422.113-r1287751-Win64) x64

## Describe the bug

As being seen in browser's omnibox, AW supports turning into [Progressive Web App](https://en.m.wikipedia.org/wiki/Progressive_web_app).

The problem is that the tray icon can't open AW as PWA - it still opens it as browser tab, whether PWA or browser tab has been already opened or not.

The same with browser tabs - double-clicking tray icon always opens new AW tab, even if it's tab has been already opened.

## To Reproduce

1. Open any of AW's pages;
1. Double-click AW's tray icon: **NOK** - new AW browser tab opens instead of activating existing one;
1. Leave one AW tab (close others) and install it's PWA;
1. Double-click AW's tray icon: **NOK** - AW PWA window isn't being activated, and new browser tab opens instead;
1. Close AW's PWA and all it's browser tab and repeat step 2: **NOK** - AW still opens in new browser tab.

## Expected behavior

I suggest the following behavior on double-clicking AW tray icon:

| PWA installed | AW tab opened | PWA launched | Action |
| --- | --- | --- | --- |
| \- | \- | \- | New browser tab will be opened |
| \- | + | \- | Browser tab will be activated. If there are several opened tabs, the latter will be activated |
| + | \- | \- | PWA will be launched |
| + | + | \- | Browser tab will be activated. If there are several opened tabs, the latter will be activated |
| + | \- | + | PWA window will be activated |
| + | + | + | PWA window will be activated |