Feature Request: add keyboard handling

[romainreignier]

I don't really need this feature but it was not clear in the documentation if the Keyboard part belongs only to Android or is shared with the Desktop app.

After testing and reading the source code, the Desktop app does not have any key press handling.

I have tried a bit and in the Javascript, we can handle the key press events, see my fork.

But I am not sure how to handle the Left and Right arrows because we need to pass the events to the iframe.
For this, we have the postMessage() available but some custom code is needed in the iframe (ImmichFrame Web) to receive these messages.

We could also set the focus to the iframe, which should receive the key press events but we would loss the ability to open settings or close the Desktop App because these actions are specific to the Desktop app and not known from the iframe app.

Lastly, with my current implementation, if we click with a mouse on the arrows to move next / previous or pause, we set the focus to the iframe and then, the key events are then handles by the iframe, so the right/left arrows works natively but the Up / Down do not work anymore.

This is a bit tricky and I am not sure if this feature is needed for now and worth the effort?