[Feature]: UI Mode - Auto run tests

### 🚀 Feature Request

To be able to run tests automatically (instead of an explicit start) using UI mode

Detailed requirements:
* If set, works with `--ui` flag or `--ui-host`/`--ui-port` flags
* Respects test configuration (i.e. tests run the same as they would with `npx playwright test`)

### Example

`npx playwright test --ui --auto-run`

CLI Documentation:
`--auto-run`: 'When running in UI mode, starts running tests when first started"

### Motivation

I want to be able to run this command and see the progress my tests on a CI

Today, the ui mode will load, but it requires going into the interface and clicking the ▶️ icon
This would remove that extra step and runs the tests

Start with the CLI documentation entry for `--auto-run` and the startup path used by `--ui`, `--ui-host`, and `--ui-port`. Confirm that the option starts tests automatically in UI mode and that execution matches `npx playwright test` while respecting the test configuration.

Written by the indexing model from the issue text.